LIBRARY OF THE
UNIVERSITY OF VIRGINIA
FROM THE BOOKS
OF
Bruce D. ReynoldsINTRODUCTION TO THE STUDY
OF
ANIMAL PARASITES AND PARASITISM
WILLIAM A. RILEY
University of Minnesota
Copyright 1927
WILLIAM A. RILEY
Mimeographed and Printed by
EDWARDS BROTHERS
ANN ARBOR, MICH.QL
137
RAS
\OR7
Copy |--- PREFACE ---
This booklet is not intended as a comprehensive text
on the subject of parasitology. It is essentially an ex~
pansion and revision of the author's "Notes on Animal
Parasites and Parasitism’” published in 1912, presenting
the outlines of an elementary and very brief cours? on the
subject. While the illustrations are to a consid¢rable
degree from the field of human parasitology or from border-
line fields, the subject is treated primarily from the
biological viewpoint.
Any such course ‘must be under heavy ov'igations tw
the classic works of Leuckart, Cobbald, Raililety,
Blanchard, and Braun, Brumpt and other ciouse.s in the
field and to the early work of Stiles, “avd, Ransom, Lav,
and their staffs in this country. One of its most im:
portant functions is to put the student in touch with
current work in the field of animal parasitology. To this
end, lists of important journals and comprehensive texts
are supplemented by those of various bibliogravhic aids,
auch as indices and abstract journals,
Owing to limitations of space, the list of special
papers is merely suggestive. The articles cited ‘are wide-
ly available and in many cases include reviews cf. the
literature and bibliographies. Much of the fundamental
work appears in foreign publications and, as in all -
scientific work, a knowledge of at least French and German
is invaluable to the student. It is urged that the op-'..
portuni ty to become acquainted with original rapers treat-.
ing of the subject be improved whenever possible.
1698
.
®.INTRODUCTION
Povular attitude
course. The more
graphic aids.
GENERAL PART
Definitions. tr
parasites, Revie
parasites, Lif
Reproduction.
par asites on thei
cl At sure Of paras
i
mination of paras
i
Jo
parasitic infect
C
Classification,
PROTOZOA
Class RHIZeroDa:
Glass MASTIGOPHORA
es cnet aes,
Herve tomon
e thi
es Chilonast
ty der Et Why? pie ep ft
Kh th SI AS PRS TS
towards parasites. Object of the
important text-books anc biblio-~
ucture of the paras’ te. Oceurrence ot
: oo
views regarding the origin of
hintory uf parasites, opectit ci ty.
ortals of entry to the host. Action: of
ir nost. Reaction of the host. Nomen-
eis aiseases. Economic value. Deter-
ites 1A the iiving host. Sources of
ons. Metheds of control. Origin.
‘Endamoebae of man and animals,
be.
t
NO
te
cia; Trypanosoma: we shmanias
Lx$ Glardia, |
<4
*
Ry
oc
99
be
}.
iS
a
3
3
§
we
tis
CO
|
}
8
te
“ee
e
ig
<
oO
eT
ct
Re
t -
G
ty
cs
{8
N
~J
Class SPOROZOA
Monocystis;
tiroplasmna;
RICKETTSTA BODIL’
SPIROCHABTA
PLATYNELMINTHES
Oe et. wet. watt et
‘ " Vr ny iy t
Class TREMA TODA
Sere ate Mena
Monogenea:
wee
=. :
Digenea:
See
H>
O
Himérias lsospora; Plasmodium;
Sarcocystis
SOR VLonorcnhis; Opisthorchis:
S; Metagonimus; Clinostomun:
Si
D . 2
te aeonAD nus; Schistosoma. Larval
eeeTABLE OF WORT ED TS (Contd)
Page
Class CESTODA 65
Monozoa
Merozoa: Taénia; Hymenolepis; Dipylidiun;
Diphyllobothrium; Echinococcus;
Multiceps.
NEMATEERLMINTHES 76
Class NEMATODA 76
Key to superfamilies
superfamily Ascaroidea w9
Ascaris; Toxacara (Belascaris); Ascaridia;
Heterakis,
Superfamily Oxyuroidea 82
Enterobius (Oxyuris); Syphacea.
superfamily Strongyloidea 83
Necator; ancylostoma; Uncinaria;: Syngamus
superfamily Dicctothymoidea 87
= Dioctophyme (ius trongyTus }
Superfamily aenneaaae 88
Trichinella;"Ttrichuris; Eucoleus; Hepaticola;
Capililaria.
Superfamily Spiruroidea 92
Gongylonéma; Habronema; Acuaria.
superfamily Filaroidea 93
Pilaria; Loa; Dracunculus; Dirofilaria.
Superfamily Rhabdisoidea 96
trongyloides; Rhabddias
Sub-class Gordiacea 97
Class ACANTHOCE PHALA 97
HIRUDI NEA 98
BIBLIOGRAPHY 99
1608‘ Fi ss = ii—-_
INTRODUCTION .
POPULAR ATTITUDE TOWARDS ANIMAL PARASITES. - To the layman,
parasites constitute a group by themselves, few in number and
objects of loathing. Until comparatively recent years even Zo-
ologists omitted them from discussion. Today the viewpoint is
radically changed. Even the average educated person recognizes
that there are other parasites than lice or tapeworms, while z0-
ologists, medical men and others interested in public health
questions recognize thet some of the most important problems in
their fields 2re those relating to animal parasites.
OURSE. - Primarily, this course is devoted
a biological viewpoint - a consid-~
of life histories.
we,
ALi
oO
eration of relationships and
Methods of control must be based on such studies. Tllustra-
tions are afforded oy the successful efforts to control malaria,
hookworm disease, and trichinosis which have followed the work-
ing out of the life cycle of the causative organisms.
Species of economic importance and especially those affect-
ing man Will be discussed when they serve for illustrating the
voints under consideration. At times a species of no apparent
economic importance will be selected because consideration of its
life history or habits may best aid in an understanding of those
of more specialized forms.
The relation of parasites to disease is an important phase
of the subject whicn can only bé touched upon. The pathology and
therapeutics of parasitism lie in the fieid of medicine. 50 al-
so, the wide series of plant parasites, including pacteria, is
omitted.
THE MORE IMPORTANT TEXT BOOKS AND BIBLIOGRAPHIC AIDS.
The most important object of this Introduction is to open
wp the field of animal parasitology and to put the student in.
touch with what has been done and with-the constantly increasing
mew developments. To this end, references to important papers
will be given, by author and date, throughout the text. Such of
thesé as cannot he included in the limited bibliographies of this
text, can be found by the aid of the standard bibliographic aids
listed below. In the following lists, the most available satisfac-
tory texts are indicated by an +.
@
Comprehans*ve Text
*Brumpt, E., 1927. Precis de parasitologie. 4 ed., viii + 1452 pp.
Preci
Paris: Masson et Cie.“Braun, M. und Seifert, 0., 1925-6. Die tierischen Parasiten
des Menschen. 6 ed. 2 vols. 1198 pr. (Second volume con-
siders clinical and ther rape sutic aspects.) Leipzig: Kabitsch.
Carazzi, D. 1922. Parassitologia animale. 2 ed. xi + 467 pp.
Milan: Socicta Editrice Libreria.
Castellani, A. and Chalmers, A. J., 1919. Manual of tropical
medicine. 3 ed. 2436 vp. New York: William Wood and Co.
“Chandler, A. Ge. 1926. Animal parasites and human disease. 3 ed.
xiii + 573 pp. New York: Nesey anc Sons
Davaine, CG. 1860. Traite’ des entozoaires et des maladies vere
mineuses de l'homme et Ges animaux conecsticues xix + xcii
+ S358 pp. Paris: Bailliére et Fils. (A rich atorehouseé of
historic interest.)
Fantham, H. B., Stephens, J.W.W. and Theobald, F.V., 1916.
Animal perasites of man. 900 pp. New York: William Wood
and Co. (Based on the 3 ed. of Braun.)
lebiger, J., 1923. Die tierischen Parasiten der Haus - und
Nutztiere. 2 ed. xvi + 440 pp. Leipzig: Brebmuller.
Gedoelst, L., 1911. Synopsis de parasitologie de l'homme et des
animaux domestigquss. xx 332 pp. Bruxelles: Lamertin.
Leuckart, K.G.F.R., 1886. The parasites of man and the diseases
which proceed from them. Trans. ot WaBe Hoyle. xxvi + 771
pp. Edinburgh: Pentland. (A classic, invaluable today for
its biological 1 vViewpoins.)
#Manson, P., 1925. Tropical diseases. 8 ed., edited by Manson -
Bahr. xx + 895 pp. New York: William Wood & CO.
Marotel, G. 1926. Parasitologie vétérinaire.
Mense, A,.W., Handbuch der Tropenkrankheiten. 3 ed. in course of
publication. Leipzig: Barth. |
Neumann, L.G., 1892. A treatise on the parasites and parasitic
diseases of the domesticated animals. Transl. and edited vy
George Fleming. xxiii + 800 pp. London.
Neumenn, R.O. and Mayer, M., 1914. Atlas und Leh
tierischen Parasiten und ihrer Ubertrager. v vi i
col. pls. Munchen: Lehmann.
Neveu ~ Lemaire, M., 1912. Parasitologie des animaux domestiques.
ii ¢ — pp. Paris: lLamarre et Gie.
we ee ee ee ee eee 1921. Précis de rarasitologie humaine. §&
ed. vi + “466 pp. Paris: lLamarre.
Railliet, A., 1895. Traitd de zoolorsie medicale et agricole.
2ed. xv +1305 pp. Paris: Asselin & Houzeau.
Underhill, B.M., 1920, Parasites and varasitosis of domestic
animals. xix + S79 pp. New York: Macmillan.
Verdun, P. et Mandoul, A.H., 1924. Précis de parasitologie
humaine. S ed. vi +:957 op. Paris: Doin.
PAC UN i x TOUE
a
Valuable information regarding tee s often to be Oob-~
tained from svecial monographs. The following handbooks are con-
venient for ready reference.
L608.5 .
Braun, M. and Lithe, 1910. A handbook of practical parasitology.
ingl. transl. by Linda Forster. vil + 208 pp. New York:
William Wood & Co. .
Daniels, C. W. and Newham, H. B. 1929. Laboratory Svucies in
tropical medicine. 5 ed. xiii + 576. London: gohn Bale,
Sons & Danielsson. — .
#Heener, R. W., Cort, “. W., and Raot, F. M., 1923. Outlines of
me@ical zoology. xv +175 op, New York: Macmillan. |
#Langeron, M., 1925. Précis de micrgscopice. 4 ed. Xv + 1034 pp.
Paris: Masson et Cis. ae
Langeron, M. et Rondeau ou Noyer, My, A9G6 » Coprologie
microscopigque. i126 pp. Paris: Masson et Cie.
Stitt, E. R., 1925. Practical vaeteriology, blood work, and
animal parasitology. 7 ed. xv + 766 pp. Philade Lphia:
Blakiston & Co.
PERIODICALS
Meny of the most important contributions dealing with
parasites apoeer in periodicals deveted to gen mneral zoology or to
human ov veterinary medicine. The fqllowing journals are more
svecifically in the field of parasitolory: - “
American journal of tropical medicime. Vol. 1, 1921.
Baltimore.
Anneles de parasitologie humaine et comparée. Vol. 1,
1922 ee Paris.
Annals of tropical medicine and varasitology. Vol. l,
1907 - Liveroool,
Archiv fur Naturgeschichte, Vol. 1, 1855 - .
Archiv fur Schiffs - und TPronen - Hygiene. Vol. 1
1897 + Leipzic.
Archives de parasitologie, Vol. 1, 1898 - Paris.’
Centralblatt fur Bakterliologie, Parasitenkunds, und
Infektions-krankheiten, Vol. es L887 - Jena. .
Journal of Helminthology, Vol. 1, ive2 - London.
Journal of Parasitology, Vol, 1 1914 - Urbana, Til.
Parasitology. Vol. 1, 1908 » QGambridge.
Société de la pathologie exotique. Bulletin. Vol. 1,
1908 - Paris.
3
*
B
Abstract Journals
Abstracts of bacteriology. Vol. 1, 1917 - Baltimore.
*Biological abstracts. Vol, 1, 1926 « Philadelphia.
uCentrelblatt fir Bakte riologis, Parasitenkunde, und
* ““Infektions- krankheiten, Vol. 4, 1887 « Tena.
(Beginning with vol. 3], 1902, the abstracts are
published as a separate. vart. j
Experiment station record. Vol. 1, 1889 - Washington.
0
1608
PERE rereBein
sInstitut Pasteur. Bulletin.” Vol. 1,1903 - Paris.
Revue générale de medecine yeterineire. Vol. i, 1903
- Toulouse.
“Review of applied entomology. Series B. Medical ana
' Veterinary. Yol.1, i916 - London.
Review of bacteriology, protozoology, and general
parasitology. “Vol. 1, 1912 ~- London. -
#Tropical.diseases bulletin. Vol. 1, 1912 - London.
Tropical veterinary bulletin. Vol. 1, 1912 - London.
Indexes
Agricultural index. Vol. 1, 1916 - New York.
Bibliographia zoologica. Vol. 1, 1896 - Leipzig.
Concilium bibliographicum (cards) 1896 - Zurich.
Index + catalogue of medical and veterinary zoology.
Authors. 1902 - 1912 - Washington.
Subjects: -Trematoda 1908; Cestoda 1912; Roundworms 1918
Protozoa of man 1925.
Index = catalogue of the Surgeon General's Library.
1880 - Washington. S
Index médicus. Vol. 1, 1879 - .
Tinstow, 0. von. 1878. Compendium der Helminthologie.
Ein Verzeichniss der bekannten Heliinthen die frei |
oder in thierischen KUrper leben, geordnet nach ihren
Wohnthieren, unter Angabe der Organe, in denen sie
gefunden sind, und mit Beiflgung der Litteraturquellien.
xxii + 382 pp. Hanover. |
1889. Nachtrag - Die Litteratur der Jahre 1878 - 1889.
xvi + 151 pp. -
Quarterly cumulative index to current medical literature.
Vol. 1, 1916 ~- Chicago. |
Royal society of London. Cataiogue of scientific papers,
1800 - 1900. Vol. 1, 1867 - London.
Zoological record. Vol. 1, 1864 - London.
16085
GENERAL PART
Definitions
PARASITE. - The term "“nerasite” is not readily defined. While
ea
often given as “An organism which lives at the expense a
another", this definit ion is applicable to @ pr nedatory species,
or, in its broadest sense, to all living organisms. For our
purposes we may say:-
A parasite - 48 an organism which, during the whole or a part
of its fife, lives on, “Gr in, in, the bory of another ¢ Organism, of
different species, from wonton 2G. obtains its sustenance.
PARASITISM, then, is “the condition of life normal and
necessary to an organism which feeds at the expense of another,
lied the host, without destroying it, as does the predator its
prey."
Illustrations of various degrees of parasitism are afforded
by the malarial parasite which passes its entire existence in some
other organism; the bot-fly which is parasitic only in the larval
stage, in the stomach of the horse; the flea which feeds on its
host only as an adult, or the tapevorm “hich is parasitic through-
out its cycle, except | for a vortion of the embryonic stage.
PREDATORY SPECIES differ in thet they live on organisms
smaller than themselves, and immediately kill their prey. There
4s not a’ sharp line to be drawn between the predaccous and the par-
asitic habit. Some forms exhibit both relationships, or, for ¢x-
ample, lecches which may kill and fecd on smaller invertebrates,
but are parasitic on the highcr animals.
SAPROZOA (loosely, seprophytes) are eee from par-
asites in that they live on decaying organic matter. Here, too,
it is impossible to draw a hard and fast line and there is much
evidence that one of the lines of development of the parasitic
habit is through these forms. :
Parasitism involves a dsfinite and essential: relation bc-
tween individuals of two species. Such a relationship is symbiosis.
SYMBIOSIS (syn=together; bios=life) in the broad sense of the
word, is the living together in definite and constant relation-
ship, of two dissimilar organisms.
Mutualism is that symbiotic relationship in which two svecies
living together mutually and permanently, help and support one
another. Examples, the lichen, an association of fungus and an
alga. Hydra viridis, Gonvoluta, (a turbellarian worm), and
16086
numerous other forms which owe their green color to unicellular
algae, (Zoochlorellae). This is often referred to as typical
symbiosis, the sense in which that word was first used by the
botanist de Bary, 1879. (Keeble and Gamble, 1907; Keeble, 1910.)
Commensalism is the living together of tvo species as
messmates, one party, only, profiting but the other not disadvan-
taged. Ex., Endamoeba coli in the human intestine; Pinnotherus,
a pea-crab, with the oyster.
|
ee FORMS OF PARASITISM - On the basis of position we may dis-
tinguish: - ;
I. Ectoparasites, or cendozoa, which live on the exterior of their
host or, moré rarely, in cavities which communicate freely with
the surface. Ex., various species of lice, ticks, the itch mites
and the hair follicle mites.
II. Endoparasites, those which live within the internal organs, -
as do tapeworms, blood parasites and the like. Intergrading
conditions are represented by the above-mentioned mites which
burrow into the skin.
"aes
On the temporal basis parasites may be grouped as:-
I. Temporary parasites, those which visit the host only at in-
tervals. EX., mosquito, chicken mite, Argasid ticks.
II. Stationary parasites, those which remain on or in the host
for considerable periods of time. Of these we may have periodic
parasites such as bot-flies, op ichneumon flies, parasitic in
only a Stage of the life cycle; and permanent parasites such as
trichina, parasitic for life.
Incidental psrasites are those which under natural conditions
are occasionally found in unusual hosts. Examples: the double
pored tapeworm,binnviidium caninum of the dog, in man; a mouse
nematode, Syphacia Obvelsta, in man.
Facultative parasites are
livin? but which arc abic te exis
introduced into the body of an
larvae of blow-flies.
no
when accidentally
t rmally free-
i:s e xh
other animal. Ex cheese skipvers,
Spurious parasites are objects which have bcen mistaken as
parasites and sometimes even been given specific names. Ex.,
plant hairs, bits of gristic, connective tissue, fungus spores,
pollen grains, etc. Grosser illustrations are reports of frogs
and lizards reported to have been voided by humans.
. 1608ry
STRUCTURE OF THE. PARASITE
te ee em SNe
shown tha
morvholor
ws
cr
2 2
@
ae
Adepta
i¢ biological.
Morphological adaotation. - With all the variety
tions to environment are nowhere more strikingly
te ase of parasites. ‘hese adaptations ere both
of struce-
ture, there are you certain Characteristic modifications which
accompany parasitic lite. As Cau liery 1919, has well
where else does structure avpear so sharply outlined 2a
+
— UN Ow
s modeled
by the kind of life, nor does preadaptation appear lens probable".
Numerous illustrations may also be found of convergent evolut ion,
Similar structures indevendently developed in widely
STOuUdS .
+e
Morphological adaptations of two general types:
separated
A. - Degencrations. TIliustrated by the reduction of organs
of locomotion, as loss of wings in parasitic insects;
and other appendages of crustacea; fusion of body soamonts; “Loss
Or cilia.
Correlatcd with these reductions are changes in
systom. Parasites often exhibit marked reduction of
the muscular
the nervous
System and sensory organs. Extreme cases are illustrated by the
loss of the alimentary canal in Cestoda and Acanthoce
chala and
still more by the changes undergone by various crustaceans
parasitic on fish.
B. ~ Neoformations. Structures may be newly de
the form of Organs of a peaehnont as, modified tarsi
inhabiting mites and lice; sucke 13 and hooks of tapow
reloped in
of heir
orms and
flukes. bauivalent st egecuncs are tc be seén in protozoan
parasites. Adaptations in soxual organs sre illustrated by
hermaphroditic forms.
Biological adaptations. - Of the various biologi
cal
adaptations Shown by parasitic forms, one of the most intcresting
is that of specificity in rela tion to their hosts, a
topic to be
discussed later. Another is that tvpe of tropism dosignated by
Brumpt, as.a specific histotropism, which directs the entering
parasite to a particular tissue or organ of the host.
If the
choice is iess limited, the term indif fferent Histotropism is
applied.
fy ro TH. PAYOR ™ A Tt is Ci
CCURRENCH OF PARASITES
Practically all animals, from amoeba with parasites in its
nucleus and its body protoplasm, to ma are subject
Leuckart, '76, lists 33 animal parasites of man, now
known. The dog is known to harbor some 200 species,
about loo.
L606
tO. attack,
over 500 are
the cat8
Hyperparasitism. - Parasites themselves may be infected by
other parasitic Species which are then known as hyperperasites.
Examples are afforded by a protozoon, Nosema heiminthorum Ln
the tapeworm, Moniezia expansa, and numerous illustrations from
insect parasites. these forms by attacking the parasites of in-
jurious species, themselves become injurious from the viewpoint
of man. Dean Swift, nearly two centuries ago, expressed a
broader truth than he suspected when he wrote:-
"So, naturalists observe, a flea
Has smaller fleas that on him prey
And these have smaller still to bite'cn,
And so proceed, ad infinitum."
Numbers which may occur in a single host. - This is devend-
ent on the species of parasitc. There is rarely present more
than one of the pork tapeworm, Taenia solium, or of the beef tape-
worm, Taenia saginata in man. On the other hand, upwards of a
hundred of the still larger fish tapeworm, Diphyllobothrium latum
ave been noted. It is not wncommon to find over a thousand
tapeworms in a chicken. Over six thousand hookworms have becn
recovered from a single patient.
Of larval forms it has been estimated that in a severe case
of trichinosis over sixty million of the worms may be present.
Of Protozoa, the numbers are beyond conception - it has been
conservatively estimated that at least one hundred and fifty
million malarial parasites must be present before the clinical
symptoms of the discase are manifscst.
| Concurrent infection by two or more specics in the same
individual 18 very common. For man, as many =s five different
species of intestinal worms at a time have been reported
(Riley, 1912).
Location within the host. - As might be expected, the larger
number Of species Occur On the surface of their host, or in cav-
ities opening to the surface, such as the alimentary canal, res-
piratory, and urinogenital passages. Other species are found in
muscles, connective tissue, nervous tissue, the blood and the
lymoh. They may live free within a cavity, or in cells, and even
in cell nuclei, as for example, Sphacrita endamoebae Becker, 1926,
or Nuclecphaga amoebae Dangeard, l8Yo.
EARLY VIEWS REGARDING THE ORIGIN OF PARASITES.
The theory of abiogenesis, or spontaneous generation, ac-
cording to which living organisms originate from non-living mat-
ter was taught by the early zoologists and in some forms -is
16089
popularly believed even today. The work of Redi, in 1668, on
the origin of maggots in meat conclusively demolished the theory
in so far as it concerned the non-microscopic free-living forms,
but zoologists were long unable to account for the presence of
perasites in the interior of the pody. Until well into the 19th
century it was believed that tapeworms originated from the mucous
of the intestine, or from partially digested food, and that itch
mites in the skin of man were the result of “bad blood". The
theory of the inheritance of parasites was also invoked to ¢ex-
plain their presonce.e
The theory of biogenesis, or development from preexisting
living forms was extended to the parasites by the beginning of the
T9th century, but most authoritics then be jeved that such forms
originated from free-living protozoa, and other free-living forms,-
the theory of hetcrogenesis, or chence development from wholly
different specics. ee .
The development of the: experimentcl method of study furnish-
ed the Key to tho problem. Feeding experiments with tapeworms
by Kuchenmeister, 1851; followed by similar work by Van Beneden,
Leuckart, Cobbald and many others, opened up the whole field of
modern parasitology.
LIFE HISTORY OF THE PARASITE
"Tf we only kmow concerning a certain animal that it is a
parasitc, we know but little; thoroughiy to understand its his-
tory, we must follow out all the scparate stages and conditions
of its existence, and cspecially the circumstances under which
it becomes a parasite.” - Leuckart, '36 p. 42. 3
As regards relation to host parasites may be grouped as3-
TA) WMonoxenous parasites (monos=one; xenas=host), such as
require only one host to complete their development. As Brumpt
has emphasized, these are of human parasites the cosmopolitan
forms, since they have accompanied man everywhere that the tom=
porature is sufficient to assure their devolopment. :
(B) Heteroxenous parasites (hetcros=different; xenas=host),
such as pass different stages of their lives in different hosts, -
usually belonging to different genera, and often widely distinct.
Their distribution usually depends on the distribution of their
intermediate hosts.
: Intermediate host. - This term is applied to the organism
which supports the asexual or immature form of the parasite. It
is somctimes called the secondary host.
Definitive host. - The hosts which supports the sexually
ERAT ON eR ee . . e
mature torm 18 known as the dcfinitive or primary host.
160810
Rssential host. - This term is a convenient one, which is
non-commital as to the particular stage of the parasite concerned.
VO
Method of transfer. - In many cases, the transfer of the «
parasite to the host is passive, the embryo being taken with food
or drink, or being injectea with the saliva of a blood-sucking
temporary parasite. The first type is known as: the ingestivé
method, the second, the-inoculative. Of the latter type, are casés
in which the organisms are found in.the excrement or body fluids
of the arthropod host, and are inoculated by the scratching of the
victim. Contrasted with the passive method is the active transfer
as illustrated by larval hookworms boring into the skin.
Alternation of generations, or metagenesis, the development ;
of one or more asexual generations followed by a sexual generation,
4g very common among parasites, (ex., malarial parasite in man aud «
in Anopheles mosquite). 3 ; , Nv
SPECIFICITY OF PARASITES oF
+ Many species of parasites are limited, normally, to a single
species of host, that is, they exhibit host specificity. So common
“is this that there is a tendency on the part of Inexperienced
workers to determine their specimens by reference to a host index. . 3
However, the immature Echinococcus, or hydatid tapeworm, is known
to develop in over forty different mammals; trichinae thrive eoual-
ly well in man, pig, rat and a wide series of animals, and many
similar illustrations could be cited. 2 7
More puzzling are cases where morphological distinctions are |
lacking, or within the range of variability, but where experimental |
transfers from one host to the other have failed. In an increasing |
number of such cases, as for example, that of Hymenolepis nana, the
dwarf tapeworm of man and the rat and mouse, repeated attempts —~
have yielded occasional positive results. pe 1
In a valuable discussion of the host specificity in both plai »
and animals, Sandground 1925 (Jour. Parasitology, 12:68) says, "{t
seems that the restriction of a population of parasites to a
particular host species for a great number of generations leads to
a special adaptation towards this species and 4 corresponding loss
of adaptability towards other hosts. This loss may only be |
temporary but if the parasite be restricted for a sufficient number |
of generations the probabilities are. that the loss will be per-
MANENG. .. see ecee sor enrccsencrsrceress«' The situation among nematode ~
parasites of animals is, I believe, closely analogous. to that
which obtains among nematode plant parasites." See, also, the very
suggestive paper by Chandler, 1923.
1608ae
ae
THE REPRODUCTION OF PARAST TES
The complicated life cycle of many parasites is a dis-
advantage in thet it enornously lessens the chances of the
species perpetuating itself. This handicap is met in various
ways, of which the following will serve as illustrations.
Great fertility is typical. - 1t is es stimated that Taenia
saginata, the veer tapeworm 0 orm Of man, produces 150,000, 000 eggs
per year, about three hundred times its body weight. A single
female of the hookworm. Necator americanus, discharges some
9000 eggs daily (Stoll, 1925) whi le the output of the other
common hockworm of man is some 45000 eggs per day (Sweet, 1924).
The usual method of diagnosing the presence of intestinal and
liver parasites by microscope examination of minute random
sampling of the feces, is based on the enormous production of
eggs and of cysts by the various species present. Other
parasites, notably certain insects, and the hydated tapeworm,
Eehinococcus granulosus exhibit polyembryony, or the develop-
ment of many individ Tuais from a single Gea.
Resistance of various developme ntal stages to unfavorable
conditions. - various parasitic protozoa have developed a
featstant spore stage in which they are protected when out of
their host; tapeworms, whipworms, ascarids and many other forms
have thick-shelled, resistant eggs. Those of Ascaris lumbricoides
of man have been preserved in viable form in earth for five years,
or, they will remain alive in strong formalin and other chemical
solutions for months (Yoshida, 1920). Eggs of a common roundworm
of chickens will survive for upwards of a year in freezing tem-~
peratures (Riley and James, 1921). Illustrations of this nature
show the futility of the attempted soil sterilization by sprink-
ling it with weak solutions of corrosive sublimate, or of
sulphuric acid.
Larval hookworms have been kept alive in the soil for
months. Dufour (1833) kept bed-bugs for a year in a closed vial,
without food. Argas miniatus, a chicken tick, has been kept
similarly in our laboratory for four years, and then was acci-
dently killed.
Herma phroditism is commonly met with in parasites, thus
providing for the perpetuation of the Species by a singic
individual.
eee mer eee
PORTALS OF ENTRY TO THE. HOST
The ways in which the parasites gain entrance to their host
are variable. The chief portals of entry are the;:-
160812
1. - Alimentary canal, with food or drink, or from soiled
fingers, toys, fondling of enimal pets, and gsophagy, or the
dirt-eating habit. This is the ingestive metnod. ? ;
2. - Skin, by active penetration, as sarcoptic mites, hookworm.
larvaé, Cereariae of blood flukes; or, secondarily, by scratch- _
ing of the patient as in the case of the spirochactes of relaps-~-
ing fever.
3. - Blood, through the bites of ectoparasites, - ticks and Rocky
Mountain spotted fever; mosquitoes and malaria. In contrast to
the ingestive method this is known as the inoculative.
4. - Prenatal infections are known to occur by the hookworms of
man and animals; ascarid worms; malaria and numerous other In-
Stances among the Protozoa.
5. - Other exceptional vortals are the resoiratory passages,
urinogenital apoaratus, the ear, and the conjunctivia.
ACTION OF PARASITES ON THEIR HOST
The history of parasitology shows extremely divergent views
as to the sxtent of the injuries caused by parasites. Early
opinions attributed most of the ills of man to helminths. The
work of Pasteur and Koch served to focus the attention of medical
men everywhere on bacteria and for years the tendency was to
attribute all diseases to these organisms. Renewed interest in
the grosser parasites followed the studies on trichina and on the
tunnel disease which Perroncito, 1880, showed to be due to hook-
worm infection. Still later came the recognition of the important
role played by protozoan parasites and by the arthropods as
carriers of disease. Today it is universally recognized by
Students of the subject that animal parasites must be reckoned
with as causes of some of the most devastating diseases of man
and animals..
The action of the parasite is dependent not only upon the
species concerned but also upon the age, the physiological
condition and cven the racial characters of the host.
Parasitism may be latent, the organisms remaining for long
pian mma
periods without manifesting themselves and suddenly, under some
peculiar condition of the host becoming active. Such, for in-
stance, is the case with malarial or amoebic dysentery infections.
Of the various ways in which the parasite may affect the
host, we may note; - :
1. = Drain on the nourishment. - While this is popularly overesti-
mated, it may be of considerable importance when large numbers of —
the parasites are present or when they are vrimarily blood-suckers,
2. - Destruction of tissues. ~ The Texas fever parasite, Babesia
bovis, may wreak down aS many as two-thirds of the red blood Cor-
puscles of its host; Coccidia destroy the liver cells and the in-
testinal epithelia of rabbits; the Giant Kidney Worm, Dioctovohme
renalis, renders the kidney of its host a mere shell.
160813
3. - Mechanical disturbances. - These may be by obstruction or
py vressure. Of the former, an instance is afforded by the
filarial worms which by blocking of the lymph channels cause
elephantiasis, or by Ascaris lumbricoides in the gall duct or,
in large numbers, cauSing intestinal impaction. The effect of
pressure is often very manifest in the cases of the development
of hydatid cysts (Echinococcus) in the liver or other organs.
4, - Irritation and inflammation. - The presence of parasites
may irritate the tissue and stimulate it to abnormal growth,
producing cysts such as those of trichina, or the capsules
surrounding cysticerci of various taveworms, or the intestinal
nodules produced by roundworms of the genus Oesophagastomum, in
sheep, cattle and hogs. Of special significance is the fact
that a cancer of the stomach in rats is induced by a roundworm of
the genus Gongylonema (Fiebiger, 1915).
5. - Production of centers of infection. - Injury to the skin by
biting or piercing forms not infrequently leads to secondary in-
fections. Similarly, intestinal parasites may lacerate the
mucosa and permit the entrance of typhoid bacilli or other
onthogens. The perforation of the intestinal wall by Ascaris
often results in peritonitis, while wandering hookworm larvae or
treichinae may carry bacteria with them to the inner tissues.
6. - Production of specific poisons. ~ The parasite in its metabo-
lism may produce specific poisons which are injurious to the host.
Such, for instance, are produced by the malerial parasites, the
trypanosome of sleeping sickness, Ascaris, and the fish tapeworm
of’ man. .
47, - Nervous reactions. ~ Characteristic nervous symptoms may ac-
company certain oarasitic infections as, for example, itching of
the nose apparently due to pinworms (Oxyuris); hysterical symp-
toms.which have been relieved by discharge of ascarids; resplira-
tory disturbances due to the presence of the giant kidney worm
in the abdominal cavity, or the intense irritation caused by the
presence of the gape-worm in the tracheae of chickens.
8. - Danger from intermittent parasites. - Far from being mere 4an-
noyances, intermittent parasites are among the most dangerous of
the group, since they often carry and disseminate pathogenic or-
GANLsins a :
REACTION OF THE HOST TO THE PARASITE
oe eS ee (eee teen eee set mee
While the parasite is able to injure its host in various
ways, there are certain reactions of the infected organism itself
which must be considered. This phase of the subject has been
elaborated by Brumpt, 1923, who groups the methods of defense as
{A) the cellular elements, mobile or fixed, and (B) the proper-
ties of the body fluids.
A. - Gellular reactions provoked by the parasite. - These
may be: in?iammatory, motadlastic, hyperplastic, end neoplastic.
1608EE terete cose nm ns
14
Inflammation is marked by more or less abundant exudation
of blood serum, by the collecting of various types of white blood
cells, or leucocytes, and often by the formation of a connective
tissue capsule about the parasite; 4s illustrated by the larvae
of tapeworms.
Metaplastic changes are characterized by the metamorphosis,
or change, of One tissue into another. Brumpt cites as an illus-
tration the transformation of the normal cylindrical epithelium
of the bronchi into a stratified pavement epithelium in cases of
pulmonary infection by flukes of the genus Paragonimus »
Hyperplastic changes are those in which there is an ab-
normal multiplication of the tissue elements, such as is found in
the epithelium of the gall ducts in trematode infections of the
Liver. :
Neoplastic reactions are those resulting in tumors, or morbid
growth more or less distinct histologically from the tissue in
which it oceurs. Most of the so-called tumors caused by parasites
are not true tumors but are connective tissue growths more proper-
ly classified as types of inflamation.
B. ~ Humoral reactions. - The presence of parasites in the
pody of an animal tends to develop in its blood serum, or other
pody fluids, certain specific substances, or properties antagonis-
tic te the invading organism. These substances are called
antibodies and the foreign protein, in this case the parasite or
its products, is called the antigen. In many cases and, particu-
larly, if the parasite is not normal to the particular animal,
these antibodies suffice to destroy it. On the other hand, in
rare cases, certain of the substances may even sensitize the host
and then produce serious effects or death, from anaphylactic
shock. An illustration is afforded by Hadwen's, 1917 studies on
the effect of improper removal of grubs, or warbles, from cattle.
NOMENCLATUR@ OF PARASITIC DISEASES
ener
Parasitic infections are designated technically by the
generic name of the causative organism, with the suffix iasis or
esis, as, taeniasis, ascariasis, trichinosis, pediculosis.
Such names do not necessarily follow changes in the zoologi-
cal nomenclature. For example, the term cistomiasis is often re-
tained for fluke infections, although the old genus Distoma has
been broken uv into a large number of genera.
160815
ECONOMIC VALUE OF PARASITES
From the viewpoint of man, not all parasites are noxious,
since they may be important factors in the control of injuri-
ous species. This has proved of special significance in the
control of certain insect pests of our forest and fruit trees.
Federal and State authorities have cooperated in the introduc-
tion of parasites of imported pests and in some cases have
attained spectacular success (see Howard; 1927).
In this connection it should be noted again that hyperpar-~
asites attacking these beneficial forms are to be classed, as
pests.
DETERMINATION OF PARASITES IN THE LIVING HOST
References: - Stiles, 1907; Brumpt, 1922; Hall 1911;
Hegner, Cort and Root, 1922.
Ectoparasites. - The diagnosis of external parasitism is
usually Simple, being a question of finding the organism. How-
ever, the habits of the various parasites must be taken into
consideration as, for example, those of the body lice, which
hide in the seams of clothing when not feeding, or those of
various temporary parasites which leave their host altogether
when they have fed. Moreover, as Styles has emphasized, thei»
presence may be unsuspected because apparently incompatable
with the habits of the patient. Not infrequently the secondary
infections complicate the diagnosis.
Endoparasites. - The chief methods of diagnosis of internal
parasites are as follows:- |
1. - Accidental expulsion. - Until very recent years this was the
chief Way in whith thé presence of the grosser parasites came to
the attention of the physician or the owner of animals.
2, - Feces examination. - The chief method of the determination
of intestinal and Tiver parasites is the microscopic examination
of minute samples of feces, for protozoa and their cysts, and
eges or larvae of helminths. The sample is usually taken at
random but, in the case of protozoal infections it is often
advantageous to select bits of mucus for special examination.
In some cases concentration methods such as sedimenting and.
sieving, centrifuging, or flotation in concentrated salt solution
are necessary.
3, - Sputum. - This may reveal the presence of lung and tracheal
parasites, such as lung flukes of the genus Paragonimus, in man,
pig, cats, dogs; or nematodes in the trachea of cats or silver
fox.
1608
Se16
4. = Urine. - For evidence of kidney, bladder, and certain plood
flukes. Examples, the flagellate protozoon Trichomonas or,
rarely, amoebae; eggs of the giant kidney. worm, Dioctophyme
renalis, or of the blood fluke Schistosoma haematobiun.
5. - Blood. - This may not only reveal blood parasites, such as
malaria, trypanosomes, and filarial worms, but through the abnor-~
mal abundance of a special type of leucocytes, the eosinophile
corpuscles, may indicate the presence of certain parasites,
notably trichinae, elsewhere in the body.
6. - Biopsy, or the removal of tissue from the living host. The
method of "harpooning” or removing a bit of muscle is sometimes
of value in diagnosing trichinosis.
7, - Culture methods. - The use of cultural methods has been ef-
fectivély applied to the diagnosis of intestinal amoebae, and .-
flagellates, trypanosomes, and some of the intestinal nematodes.
A special type of cultural method is that of using the arthropod
host instead of an artificial’ medium. This has been designated
xenodiagnosis by Brumpt, 1914, who has applied it especially to
the study of trypanosomes.
8. - Serum reactions. ~ The most widely used of these tests is
the Wasserman test for syphilis, but similar methods have been
used in the diagnosis of various animal parasites, notably the
echinococcus or hydatid cysts (Magath, 1921}. :
9. ~ Clinical symptoms. - These are usually vague and little to
be relied on. in some cases they are sufficient for tentative
diagnosis.
SOURCES OF PARASITIC INFECTIONS
As will be brought out clearly in the discussion of various
parasites, the chief sources of infection are:
1, = The ground. - Hookworm and strongyloides larvae; eggs of As-
caries, sreesics. and various other nematodes which may remain
for months and even for years in viable condition in the soil,
2. ~ Water. = Protozoal cysts; eggs of various helminths; cercar-~
iae of blood flukes; various tapeworm cysts in minute crustaceans
which are accidently swallowed with water. |
Oo. * Vegetables and fruits served in uncooked condition. These
are a special source of danger in countries where human excrement
is used as fertilizer.
4, - Other animals:-
a. = Which serve as food: - pig and trichinae, or pork
tapeworm; cattle and tapeworm: fish and fluke infections.
b. ~- Pets and companions. - Double pored tapeworm of
dogs and man; Echinococcus tapeworm; mange of cats; fleas of cats
and dogs. —
c. - Ectoparasites transmitting parasites by their bites,
or, by infective excrement, or body fluids.
d. - Humans, from contact infections.
16081?
METHODS OF CONTROL OF PARASITES
Disappointment and failure have followed all attempts to
combat widely distributed parasites of men and animals by treat-
ment measures. In such campaigns preventive measures must be
the main reliance and these must be based on a thorough knowledge
of the life history and ecology of the parasite concerned. The
chief preventive measures may be grouped as follows:-
1. - SANITARY METHODS. ~ Cleanliness, both personal and civic,
constitutes one of the important safeguards against parasitic
infections. This involves proper methods of sewage disposal
sO as to avoid contamination of sofl, food, and water; fly —
control to protect food and drink from direct carriage Of. in-
_féetions; and the proper control of animal pets, since several
important parasitic diseasés Of man and stilT more of domesti-
cated animals are contracted from dogs and cats.
Meat inspection, not only in the large packing houses but
in local slaughter houses, plays an important role in the preven-
tion of human infections, and the proper disposal of slaughter--
house offal which is thus insured, is a very important means of
preveriting further animal infections with such parasites as
-trichinae, hydatid tapeworm, and others. es
@» = HEAT STERILIZATION through cooking of foods is one of the ~
most important methods of avoidance of such parasites as trichinae,.
the beef tapeworm, and of various protozoal parasites. The oft-
recommended dipping in solution of calcium chloride of fruits and
vegetables which are to be eaten raw is useless. Much safer is °
dipping for ten séconds in boiling water, or water which remains
at 80 CG. (176 F.), as recommended by Mills, Bartlett, and
Kessler, 1925, Similarly, water may be rendered safe by boiling.
Oe © REFRIGERATION of meats, under proper control, is sufficient
to kill various cysts of parasitic worms. The régulations of the
federal Bureau of Animal Industry permit beef lightly infected by
cysts of Taenia saginata passed as food after 6 days in cold
storage.
4. ~- DESTRUCTION OF ESSENTIAL HOSTS. - In many cases this 15 a
feasible and fundamentally important method of control of parasites.
Tilustrations are afforded by the destruction of certain species
of mosquitoes in anti-malarial work, and of other species, still.
in combatting yellow fever; the killing of stray dogs and coyotes
forms an important line of attack against the serious gid tapeworm
of sheep, or against the hydatid tapeworm. The Bureau of Animal _
Industry requires that all collie or sheep dogs imported into this
country be held in quarantine pending the results of fecal examina-
tion for tapeworms. oes
L60818
ORIGIN OF PARASITES
Parasitic habit not a basis of classification. - It was
long supposed that parasites constituted a natural group, the
older workers classing various endoparasites together as
"helminths",
Relation of free-living forms. « The close relationship to
free-living forms fs readily seen in many of the endoparasitic
nematodes and trematodes. In others, such as some of the
parasitic crustacea, it is clearly shown by the developmental
history. All of the available evidence tends to show that
arasitism is an adaptive phenomenon, originating independently
un widely different groups.
THE CLASSIFICATION OF PARASITES
Representative animal parasites will be considered in their
z0Ological sequence and the group characteristics will be dis-
cussed in that connection. The following list of phyla of the
Animal Kingdom summarizes briefly the groups with which we shall
be especially concerned. a ao
PHYLUM PROTOZOA
Animals in which the entire body consists of a single
animal cell,
Class RHIZOPODA - Protozoa in which the motile organs
are pseudopodia.
Glass MASTIGOPHORA = Protozoa with an outer colle
integument and in which the motile organs are flagella.
: Class INFUSORIA - Protozoa with an outer céll-integument
and which are always ciliated either through life or in the
young condition. ;
Class SPOROZOA + Parasitic Protozoa typically without
organs Of locomotion, and which reproduce by spore-formation,.
Group not a natural one,
Class SPIROCHAETA ~ Spiral organisms with flexible slender
bodies, diffuse chromatin and active movements often classed
with bacteria.
Phylum PORIFERA
Not discussed in this course. |
Phylum COELENTERATA
Not discussed in this course.
Phylum PLATYHELMINTHES
1608La
PHYLUM PLATYHELMINTHES
The Platodes or Flat-Worms
The flat-worms are bilaterally symmetrical animals, which
are devoid of true metameric segmentation, and which have no
body cavity between the alimentary canal and the integument.
There is no blood-vascular system: but there is an excretory
(water-vascular) system. The alimentary canal when present has
only a single opening, and is much branched.
Class TREMATODA - Parasitic flat-worms, without a covering
of cilfa In the adult state, with a well-developed digestive ap-
paratus, and with the mouth at the cephalic end of the body. The
liver-fluke is an example of this class.
Class TURBELLARIA ~ Non-parasitic flat-worms, with a ciliated
epidermes. Not discussed, ee
Class CESTODA - Endo-parasitic flat-worms, without cilia, and
without a digestive cavity; usvally becoming segmented by budding.
This class includes the tapeworms.
Phylum NEMATHELMINTHES
The Thread Worms
The body is cylindrical, spindle-shaped, or threadlike, un-
segmented, and. covered with a thick cuticle; the body cavity is
usually spacious. The sexes are usually separate, but
hermaphroditic species occur. Yorke and Maplestone recognize two
classes of this phylum.
Class NEMATODA - With an alimentary canal but without 4
proboscis.
Order Eunematoda -' Alimentary canal typically complete and
present throughout Iife, body cavity not lined with epithelium,
lateral cords present. Familiar examples are Ascaris, Oxyuris,
Trichinella.
Order Gordiacea - Larval stage parasitic and possessing an
alimentary Canal; adults free-living, without an alimentary
canal; body cavity lined with an epthelium. To this order belong
the "hair-snakes" of the genus Gordius, and related forms.
Class ACANTHOCEPHALA ~- Lack alimentary canal; possess a
protrusible proboscis which is covered with many rows of
recurved hooks.
160820
Phylum ECHINODERMATA
Not discussed in this course.
Phylum MOLLUSCOIDA
Not discussed in this course.
Phylum ANNULATA
The Syamented Worms
Bilaterally symmetrical animals with the body composed of
Similar segments or metameres, without jointed legs, and with an
alimentary canal furnished with two openings. Only one of the
Classes discussed in this course.
Class HIRUDINEA - Segments of body marked externally by sec-
ondary rings. Each end of the body is furnished with a sucker.
The medicinal leech is an example of this class.
Phylum ARTHROPODA
See Comstock's "Manual for the Study of Insects" and "The
Spider Book". ,
Bilaterally symmetrical animals in which the body is
segmented and bears a pair of jointed appendages on each or on
some of the segments.
Class CRUSTACEA - The members of this class are aquatic
Arthropoda, which breathe by true gills. They have two pairs
of antennae and at least five pairs of legs.
Glass ARACHNIDA - The members of this class are air-breath-
ing Arthropods, in which the head and thorax are grown together,
forming a cephalothorax; which have four pairs of légs fitted
for walking, and which have no feeler-like antennae. To this
class belong the spiders, ticks, mites, and others.
Order ACARINA - This order includes the mites; these differ
from other Arachnida in that the abdomen is fused with the
cephalothorax, giving the entire body a more or less saclike
appearance.
Class MYRIAPODA - This class includes the centipedes and
the millipedes, air-breathing Arthropoda in which the thorax and
abdomen form a continuous region, with from six to two hundred
segments, each bearing a pair of legs.
160821
Class HEXAPODA - Air-breathing Arthropoda, with a distinct
head, thorax and abdomen. They have one pair of antennae, three
pairs of legs, and usually one or two pairs of wings in the adult
state. This class is composed of the different orders of in-
sects:- of special significance to the parasitologist are the
following: .
Order MALLOPHAGA - This order includes the bird lice; these
are wingléss parasitic insects, with biting. mouvth~-parts; their
metamorphosis is incomplete.
Order ANOPLURA - The order Anoplura is a small group, com-,
posed of the sucking lice. They are wingless, parasitic insects
with piercing and sucking mouth-parts in the form of an invaginat~-
ed tube; the thoracic segments are fused, and the legs are fitted
for clinging to hairs of the host.
Order HEMIPTERA - This order includes the true bugs. The
winged mémbers have four wings, but certain species are wingless;
the mouth parts are formed for sucking; the metamorphosis is in-
complete,
Order DIPTERA - This order includes the flies, among which
are the mosquitoes, bot-flies, the sheeptick, and many others.
The winged members have only two wings; the mouth-parts are
formed for sucking; or for piercing and sucking; the metamorpho-
Sis is complete.
Order SIPHONAPTERA - This order includes the fleas; the mem-.
bers of it are practically wingless, the wings being represented
Only by minute scaly plates; the mouth-parts are formed for suck-
ing; the metamorphosis is complete.
Phylum MOLLUSCA
Not discussed in this course.
Phylum CHORDATA OR VERTEBRATA
Not discussed in this course.
160822
SPECIAL PART
REPRESENTATIVE PARASITIC PROTOZOA
Important General References
Butschli, 1880 - 1889; Calkins, 1909, 1926; Craig, 1926;
Doflein, 1916; Hartmann, 1921; Hartmann and Schilling, i917;
Hegner, 1927; Hegner and Taliaferro, 1925; Minchin, 1912; Noller,
1922; Prowazek, 1911; Wenyon, 1926. |
The early microscopists, in their incessant search for new
wonders did not fail to note the presence of parasitic Protozoa
in the animal body. Thus, Leeuwenhoeck (1632 ~ 1723) studied
the intestinal protozoa of frogs and, as Dobell has pointed out,
noted the oocysts of the rabbit coccidium and even studied the
flagellate, Giardia intestinalis from his own stools. About
the middle of the 19th century the presence of amoebae and of
the intestinal infusorian Balantidium coli in man was noted,
Soon after this time Pasteur was making his famous studies on the
nosema disease of silkworms, although he did not recognize the
causative organism as a protozoan. :
Overshadowed by the rise of bacteriology and by the search
for bacteria as the specific cause of all diseases, the signifi-
cance Of Protozoa as pathogenic organisms was long overlooked.
Indeed, relatively little attention was given them until the
beginning of the present century.
Now it is well-known that some of the most devastating
diseases of man and animals are of protozoal causation. Of the
many illustrations there may be cited, malaria, sleeping sick-
ness, kala-azar, yellow fever, the Texas fever of cattle, the
nosema disease of silkworms. All of the sub-phyla of Protozoa
contribute important illustrations of parasitic forms. They
inhabit organs, tissues and cells and even the nuclei of cells
of their varied hosts. Their adaptations, both morphological
and biological are comparable to those of other parasitic
Groups.
CLASSIFICATION
Without entering into the discussion of the relative rank
of the Protozoa as contrasted with the remaining animal phyla
we may accept the usual characterization of Protozoa as one-celled
animals which during some part of their life cycle exhibit
motility.
The phylum is usually divided into four classes, the
Rhizopoda, the Mastigophora, the Infusoria, and the Sporozoa.
160820
Following Brumpt we shall include in a fifth class, the
Spirochaeta, an important group of organisms regarded by some
as bacteria and by others as Mastigophora. ‘The distinguishing
characteristics of the classes are given on page 18,
RHIZOPODA
As far back as 1849 Gros discovered in the tartar on the
internal surface of the teeth of man an amoeba which is now
known as Endamoeba gingivalis. Since that time a considerable
number of species of amoeba have been reported for man and Aas
various animals among them at least one species of prime signifi-
cance as a cause of dysentery. The earlier workers supposed that
the forms parasitic in animals were free living amoebae which -
had been taken in with water and had survived as parasites. It
is now recognized that these species do not exist free in nature
but onky in the encysted stage. From the view point of human
parasitology the most important species is Endamoeba histolytica.
ENDAMOEBA HISTOLYTICA (E. dysenteriae, E. tetragona). -
This is one of several species Tying in the alimentary tract
of man. It is the cause of amoebiasis or the so-called
"tropical dysentery", a disease which is now known to be wide-
spread in temperate zones as well as in the tropics.
Location in the host. - Endamoeba histolytica normally
lives in thé stbmucosal tissue of the large intestine of man.
Carried by the circulatory system and the lymphatics it may
infect the liver, lungs, brain, and various other organs of the
body. In recent years they have been noted in a number of
cases of inflammation of the bladder (Petzetakis, 1925); in a
peculiar type of rheumatism of the joints and’ in the lymph |
glands in Hodgkin's disease (Kofoid and Swezy, 1922). As far
as the biology of the parasite is concerned all of these hab-
itats except that in the large intestine must be regarded as
secondary and abnormal. |
Description. - The active stage of trophozoite of Endamoeba
histolytica has essentially the structure of a free-living
amoeba. Typically it measures from 20 - 30 microns in diameter,
possesses one or two blunt pseudopods, and has the ectosarc, or
clear outer layer, distinct from the endosarc, or granular layer.
Imbedded in the endosare are usually red blood cells, an import-
ant aid in distinguishing this parasitic species from the non-
parasitic amoebae which often occur in the intestine of man,
The nucleus is excentric in position, small and distinct. In
Stained preparations it measures 4 - 7 microns in diameter. On
the inside of the nuclear membrane is a thin layer of chromatin
and in the center is a small dote-like karysome.
L608a4
Development. - There are two methods of reproduction of
Endamoeba histolytica. - that of simple binary fission and that
of encystment and spore formation. The first occurs in the
tissues of the infected organs, the latter by the migration of
active amoebae or trophozoites to the lumen of the intestine
where they become rounded, decrease in size and lose their food
inclusions. This is the precystic stage. By the secretion of
a delicate but impervious elastic wall sphaeroidal cysts are
formed which measure from 5 - 20/in diameter. In a given
infection the cysts may have a limited range of size there
being apparently various races of the organism.
Within the cysts the nucleus divides into two and then into
four nuclei characteristic of mature cysts of this species. In
stained cysts there are often to be found in the cytoplasm one
or more rodlike bodies with rounded ends which, on account of
oe properties are called chromatoid or siderophile
odies. |
These cysts are discharged from the body, often in
enormous numbers and are disseminated on fruits and vegetables,
in water, and by houseflies. When taken up by the human host
the cyst wall is broken down in the stomach and small intestine
and the four small amoebae are liberated and make their way into
the tissues of the large intestine.
Effect of the host. - The long-continued discussions as to
whether Bndamoeba histolytica is pathogenic to the human host
have been definitely closed by the extensive studies of recent
years. It has been established that the parasite feeds on the
blood cells and fluids of its host and that it causes extensive
thickening and ulceration of the bowel and other infected organs.
Active cases of intestinal amoebiasis are typically characterized
by severe dysentery with blood, mucus in which great numbers of
the active amoebae are to be found. In regions where it is «
common it is the most frequent cause of liver abscess. As pre-
viously noted, the parasite has been implicated in various other
diseases, Such as cystitis, brain abscess, and a type of
arthritis deformans.
There is, however, abundant evidence that infections may ex-
ist for long periods of time without causing any noteworthy clin-
t$cal effects. Such carrier cases are sources of other infections
as: well as themselves liable to acute attacks.
Occurrence in animals. - Many of the references in litera-
ture to occurrence Of Endamoeba histolytica in animals are based
on misidentifications of amoebae peculiar to the given host.
However, E- Dh ee rteace is transmissible to rats and since it is
able to complete its development in these rodents there is every
reascn to suppose that they may be factors in the dissemination
LE0825
of the infection (Kessel, 1923). Cats and dogs are suscepti-
ble to infection, but there is no clear evidence that the
cystic state is reached in these animals. Kittens are especially
susceptible and the rectal injection of human discharges con-
taining motile amoébae is one of the methods of diagnosis of the
pathogenic species. Only the cystic stage can be transferred by
feeding, as the trophozoites are destroyed by the gastric juices.
Artificial cultures. - Early reports of successful cultiva-~
tion Of Endamoeba histolytica have been largely discredited,
as due to errors in identification and to contaminations. In
1925 Boeck and Drbohlav reported the successful culture of E.
histolytica, on Locke-egg-serum and Locke-egg-albumin. Since
that time the work has been repeatedly verified and the method
has even been urged as a routine method of diagnosis (Craig
and St. John, 1927.),
Prevalence. - The idea that amoebiasis of man, or infec~
tion by pathogenic amoebae, is limited to tropical regions has
given way before abundant evidence that it is much more wide-
spread in its distribution. While especially prevalent in
India, China, South and Central America and similar regions,
it is frequently contracted in our Southern States and Europe
and cases contracted in the Northern United States are by no
means rare. The extensive war-time and post-war examinations
of home service and foreign service troops and of civilians in-
dicate that at least 4% of our population harbor this parasite.
Of these probably 95% are carriers who do not show marked
clinical symptoms. ‘
Epidemiology. - The chief methods by which the infection
passes from man to man are through the handiing of food by cyst
carriers, the use of human excrement as fertilizer, and through
the agency of houseflies. Root, 1921, observed living cysts in
the gut of houseflies up to the end of the second day after in-~-
gestion. Kessel's work, supported by that of several other
workers, shows that rats and mice also play a role in the
dissemination of the parasite.
Prophylaxis. - Theoretically the avoidance of infection is
very Simple but the necessary measures are not always readily
carried out. They consist in the protection of food and drink
from contamination by fecal material, whether through the agency
of soil, human carriers or insects, The elimination of carriers
from restaurants and kitchens is as important here as in the
case of typhoid. Proper screening and other protection from
flies, the cooking of fruits and vegetables and the boiling of
drinking water not known to be safe, constitute very essential
precautions. Fruits and vegetables which are to be taken un-
cooked may be rendered safe by dipping for 10 seconds in water
160826
maintained at a temperature above 80° C., as recommended by
‘Mills, Bartlett & Kessel, 1925.
References. - Recent years have witnessed a flood of
literature dealing with amoebic infections of man. Fortunately
excellent consideration and bibliographies are afforded by the
texts of Craig, Hegner and Taliaferro, and of Wenyon. An in-
valuable critical review of the field is that of Dobell, 1919.
In addition to these and the specific references in the above
discussion, may be cited Boeck and Stiles, 19¢5, incidence in.
U. S.; Kofoid, 1923, general, and numerous current contributions; ©
Walker and Sellards, 1913, experimental amoebiasis in man.
FNDAMORBA COLI. - This is a large amoeba living in the lumen
of the large intestine and of medical interest because it is often
mistaken for the pathogenic E. histolytica. Unlike that form it
does not feed on the host tissues and hence it rarely, if ever,
contains red blood corpuscles but takes up numerous bacteria,
food fragments and starch grains. The active forms are about the
game size as those of the pathogenic species but are. more
sluggish and have a much less prominent ectoplasm. The nucleus
is more distinct in the living trophozoite and has its karysome
excantric in position.
The cysts of Endamoeba coli vary from 10 to 30/4 in diameter
and when mature are 6 nucleate, There is usually present a well
outlined glycogen vacuole and the chromatoid bodies when present
‘are splinter-like.
ENDAMOEBA GINGIVALIS is commonly found in the tartar of the
teeth and was the first amoeba of man to be noted. It is exceed~
ingly variable in size, ranging according to figures of different
workers, from 6 to even 60/4. Wo cystic stage is known, trans~
fer apparently being by direct contact from mouth to mouth. In
the past this species has been of much medical interest, due to
the claim that it was the causative agent of pyorrhoea, a view i
again brought forward .byathe carefuliwork of Hinshaw, 1927.
ENDOLIMAX NANA (Endamoeba nana) is a dwarf form which is
nonpathogenic but which has a 4 = nucleate cyst which has
usually been mistaken for that of E. histolytica. These cysts
are typically oval, measuring 8 - TOM by 7 - 8A , and are —
characterized by having the chromatin clumped in a large blob,
rather than peripheral.
‘ BNDAMOEBAE (OF “ANIMALS. - As previously noted, E.
histolytica is transmissable to dogs, cats and rodents and prob-
ably, to other animals but many of the records of its occurrence
are due to failure to recognize that there are closely related
species peculiar to the animal host. Of these special interest
1608ol
attaches to the following, on account of possible confusion with
those of human amoebiasis: - Endamoeba ratti and Councilmania
decumani from the rat, and Councilmania muris from the mouse
=(Kessel, 1924), and to Endamoecba blattae, Leidy, 1879, from
the oriental cockroach, which is of zoological interest as the
type of the genus. A recent study of this form is that of
Kudo ; 1926,
Class MASTIGOPHORA
The MASTIGOPHORA, or Flagellata, are Protozoa which are _
provided with one or several whip-like flagellae. Reproduction
is usually by simple fission. Formation of protective cysts
occurs in many cases. The group is a large one and contains —
many free-living forms as well as numerous species parasitic in.
animals and plants. The first known intestinal parasite of man
“was Giardia intestinalis, a flagellate which has only recently
been recognized as of considerable pathologic significance.
Certain of the Mastigophora resemble plants in that they
‘are provided with chlorophyll. and may have a cellulose capsule.
-These have been placed in the sub-class PHYTOMASTIGINA to
distinguish them from the ZOOMASTIGINA which have a holozoic¢c
nutrition and are animal-like. It is the latter group which
concerns US.
* The classification of the Zoomastigina is in a chaotic
‘condition. Since Wenyon's text is destined to be for years the
standard English reference dealing with parasitic Protozoa, we
shall indicate here his subdivisions of the Zoomastigina and
then take up in zoological sequence a few illustrations either
typical or of special medical significance.
ZOOMASTIGINA
A. Monozoic Forms
There is a single nucleus and a varying number of flagella
and blepharoplasts.
1. Order: PROTOMONADIDA. - The flagella are few in
number (rarély more than six). : ;
2. Order: HYPERMASTIGIDA. - The flagella are vevy numerous,
3. Order: CYSTOFLAGELLATA. - Haeckel, 1873, - The body
is large and globular, and possesses a peculiar tentacle as well
as a single flagellum.
160828
B. Diplozoic Forms
There are two nuclei, while the flagella, blepharoplasts,
and other structures are similarly duplicated, giving rise to
a bilateral symmetry.
4, Order: DIPLOMONADIDA. - With the characters of the
Diplozoic forms.
C. Polyzoic Forms
There are more than two nuclei and numerous flagella and
blepharoplasts.
5. Order: POLYMONADIDA. - With the characters of the-
Polyzoic forms. :
The order PROTOMONADIDA is of interest chiefly because it
includes the haemoflagellates of man and animals. In addition
to these forms and their close allies, there may be mentioned «
as important members of the order Histomonas meleagris
(Theobald Smith 1905), the causative organism of the highly-
fatal blackhead of young turkeys, and Costia necatrix, a pear-
shaped, two or four-flagellated form parasitic on the skin of
fish.
The haemoflagellates and closely related forms belong! to
the family TRYPANOSOMIDAE. They are characterized by a more
or less spindle~shaped body, a central nucleus, and by the
possession Of a compound nucleus-like structure, the ©
kinetoplast, from which arises the single flagellum. The family
is Of great medical and veterinary significance since it con-
tains the organisms of sleeping sickness, Chagas! disease, and
various types of leishmaniases of man, and those of nagana and
surra, dourine, and other serious maladies of domesticated
animals. Other species are parasitic in cold blooded vertebrates
and in invertebrates, while still others may have both an
invertebrate and a plant host.
The question of the evolution of the blood-infesting
flagellates is one which has attracted much attention. Wenyon,
and numerous other investigators, consider that the trypanosomes
of vertebrates were originally purely insect flagellates which
gradually became adapted to the blood medium when the insects
became blood suckers. Moreover, from a practical view point
it is of great importance to distinguish between flagellates
peculiar to the invertebrate and those which represent a stage
in the development of a cyclic trypanosome. For these reasons
it is desirable to consider briefly two genera of flagellates,
Herpetomonas and Crithidia which are confined to invertebrate,
160829
chiefly insect, hosts and which are transferred from host to
host as cysts in the feces.
Flagellates of the genus Herpetomonas are found in the
intestinal tract of a large number of invertebrates, 4 :
typical form occurring in the housefly. The kinetoplast is
at the anterior, rounded end and there is no trace of an un-
dulating membrane. In the hind gut of the insect the
elongate motile form becomes shortened and rounded, and
surrounded by a cyst wall. It is by means of these cysts that
infection is spread from one host to another.
The genus Crithidia likewise has the kinetoplast anterior
to the nucleus but closer to this structure, and the flagellum
takes a lateral position and is connected with the body of the
organism by short undulating membrane. Many of the so-called
Crithidia are now known to be merely stages in the life cycle
of vertebrate trypanosomes (See Becker, 1925; McCulloch, 1919).
In recent years numerous workers have reported successful
Snoculations of laboratory animals with supposedly strictly in-
-sect flagellates of the genera Herpetomonas and Crithidia.
Interest in the question has been greatly Stimulated by the
discovery that herpetomonadlike flagellates are to be found in
various plants, particularly in the latex of representatives
of the Euphorciaceae. They are transferred by sucking insects.
For these flagellates having both an insect and a plant host
the generic name Phytomonas has been proposed. The question
of their relation to vertebrate infections has not been sat-
isfactorily demonstrated but offers a fertile field for
further study (See Strong, 1924; Noguchi, 1925, 1926; Noguchi
and Tilden, 1926).
Of the family Trypanosomidae the type genus Trypanosoma
is characterized by the fact that the flagellum arising from
the kinetodlast is connected with the entire extent of the
body of the organism by a delicate undulating membrane of
which it forms the margin.
The trypanosomes are known chiefly as parasites of the
blood of vertebrates but certain species may also be found in
the tissues. Most of the forms which have been studied in
detail, undergo a part of their life cycle in some inver~
tebrate, but a very important species, Trypanosoma equiperdum,
which causes a venereal disease of horses, is transmitted
directly. Owing to their virulent effect on man and animals
in Africa, they have been of outstanding interest to all of
the nations attempting colonization in that country and no
other protozoal parasite has been subject to more searching
investigation than have the trypanosomes Since the beginning
160830
of the present century. Trypanosoma lewisi is a cosmopolitan
species which has been extensively studied and which may
serve as a type.
TRYPANOSOMA LEWISI. - This species is common in various
species of wild rats the world over and is readily transmissi~
ble to laboratory rats.
Description. - T. lewisi has a more or less spindie- —
shaped body about 25 min length, and with one edge provided
with a delicate, undulating membrane. The flagellum arises
near one end, from a highly refractile granule known as the
blepharoplast and continues as the thickened end of the un-
dulating membrane, to project at the anterior end. Closely
associated with this is a larger somewhat rod-shaped structure
which is sometimes designated the kinetonucleus but more
properly the parabasal body. The combined blepharoplast and
parabasal body constitute the kinetoplast. Near the center of
the body is the principal nuclevs, or troohonucleus,
Movements. ~ The movements of T. lewisi are of two types,
a euglenoid body contraction and setond, a very active movement
by means of the flagellum. When the parasites are abundant
they may be detected under low power by the disturbance of the
blood corpuscles.
Reproduction. - The reproduction in the blood of the rat
is by longitudinal fission. The division of the body pro-
toplasm is preceded by the division of the kinetoplast and
trophonucleus and the formation of a new flagellum, paraltelling,
and closely applied to the original one. For a time the two
daughter trypanosomes are connected at their posterior end and
under some conditions the division of the cytoplasm at this
point may be delayed, resulting in the appearance of multiple
divisions, or "rosette" forms.
In addition to this process which occurs in the blood of
the vertebrate host, T. lewisi undergoes a complicated cycle
in the invertebrate host which serves as the agent of transfer
from rat to rat. The rat louse, Haematopinus spinulosus may
serve in this capacity but as shown by the work of Minchin and
Thomson, 1915, the most important vector is the rat flea,
Geratophyllus fasciatus. Within the first half hour after
being sucked up by the flea the blood in its stomach is still
infective on inoculation into a rat but after this brief
period the contained trypanosomes undergo a striking cycle of
changes and are not again infective until the end of the fifth
day. They first enter the celis of the "stomach" of the flea,
where they divide to form approximately a dozen trypanosomes
very similar to those taken up in the blood of the rat.
1603ol
These forms either re-enter cells and redivide or without
further delay they may migrate to the hind gut and rectum of
the insect. They become inactive, the body is shortened and
rounded and the position of the nucleus and the kinetoplast
become reversed, producing the sc-cslled "crithidia" forms,
Sooner or later there are produced short, stumpy trypanosomes,
very different from those of the rat, which pass out with the
feces of the insect after the fifth day. These constitute the
infective stage which thus is transferred by the excrement of
the flea rather than inoculated by its bite. Licked up by the
rat or swallowed with its insect host, the trypanosomes appear
in the blood in 6 - 7 days. The infection may persist in the
rodent for three months or even longer.
Though many authors have described sexual forms in this
and other species of trypanosomes there is no satisfactory |
evidence that the cycle in the insect can be so interpreted,
as is that of the malarial parasite in the mosquito.
“Artificial culture. - This is one of the early forms of
parasitic protozoa to be cultivated with marked success, Novy
and MeNeal, 1903, having first grown it on nutrient agar and
defibrinated rabbit's blood. Their original formula was
simplified by Nicolle, 1908, and under the name of N.N.N.
medium, is widely used for the cultivation of the trypanosomes
and related forms,
Prevalence. - While Trypanosome lewisi is a fairly common
parasite of wild rats, the statements current in literature
regarding percentages of infection have little value. Like any
epidemic disease, centers of infection exist within which there
may be a high incidence, while at a given time in other
localities the parasite may be very difficult to find.
Effects on host. = In general, this species is regarded
as non-pathogenic to the rodent host though heavy experimental
infections sometimes result in death of white rats. Once in-
fected, the rat becomes immune to subsequent infections.
Young rats are much more susceptible to infections than are
old ones, quite apart from the question of acquired immunity.
RELATED SPECIES. - Trypanosoma gambiense is the cause of
the deadly African sleeping sickness of man + a disease which
has spread widely in the tropical regions of that country since
the beginning of the present century. The organisms are found
in the blood and in the cerebrospinal fluid in the earlier
stages of the disease and are conveyed from man to man by the
tsetse-fly, Glossina palpalis. Rarely, this transfer is by
direct inoculation from contaminated mouthparts but as a rule
it is only after the parasite has undergone a twenty day cycle
1608OL
of development in the gut of the fly and is then injected with
the saliva of the feeding insect. Most of the present day
workers recognize a type of sleeping sickness as due to 4
distinct species T.:rhodesiense, transmissible by Glossina
morsitnas. In both tases there is evidence that wild animals
serve as reservoirs of the disease.
Trypanosoma evansi was the first trypanosome noted as
pathogenic. lt is the cause of a serious disease of equines,
known as surra, which is prevalent in Asia, North Africa
and neighboring islands. In order to prevent its importation
into this country the U. S. Bureau of Animal Industry has —
found it necessary to adopt stringent regulations controlling
transfer of horses from the Philippines. A similar infection
known as "mal de caderas" occurs in tropical and subtropical
South and Central America. Both diseases are conveyed
mechanically by biting flies such as Stomoxys (stablefly) and
Tabanus (horseflies).
Trypanosoma brucei is the organism of a usually fatal
disease of cattle and other domesticated animals known as
nagana. It is transmitted by the tsetsefly, Glossina
morsitans, but until the work of David Bruce, 1895, this fact
Was not even suspected and the bite of the fly itself had long
been considered extremely virulant. The epoch-making work of
Bruce had a great influence on human and animal disease.
Trypanosoma crugi occurs in the blood of man in Brazil,
Pern, san Salvador and Venezuela, causing the disease known as
Chagas! disease or South American trypanosomiasis. It presents
a very different type of development in that the parasites do
not multiply in the circulating blood but in the muscles, the —
heart fibers, and nerve cells. Here they lose their flagellae,
become contracted and rounded, assuming the so-called leishmanoid
form. in this stage they divide repeatedly, invading more and
more of the tissue. Four or five days after inoculation they
transform into trypanosomes which make their way through the
tissues and into the blood stream. When taken up by certain
Reduviid, or assassian bugs, notably Triatoma megista, they
undergo a complicated development and 8 - 10 days later are dise
charged with the feces of the insect. Infection of man appar-
ently occurs through the rubbing of the fecal material into the
wound made by the bug, though the parasites can pass through
healthy mucous membrane of the mouth or conjunctive. The
natural reservoirs of the disease are thought to be armadillos.
Trypanosoma equiperdum represents still another departure
from the better known types of trypanosome development. It is
the cause of dourine, a venereal disease of horse which is
conveyed by coitus.
1608oo
Some authorities consider that it represents a specialized life
cycle in which the insect host has been dropped out. The
disease was introduced into Europe from the Orient early in the
19th century and was first recognized in this country ia.
Illinois in 1886, being traceable to a stallion imported from
France. In spite of strenuous efforts of the federal authori-~
ties to stamp it out by killing infected animals and by
quarantine, the disease was known to exist in at least six West
Central States in 1912. - See Mohler, 1911; Mohler and
Schoening, 1920. It is now regarded as under control.
Trypanosomes are also abundantly distributed in cold-
blooded animals. Indeed, the first recorded forms were found in
the blood of trout and shortly thereafter Gruby, 1845, proposed
the generic name Trypanosoma for the forms which he found in the
blood of the frog. The best known of these fish and batrachian
parasites undergo a part of their cycle in leeches.
References. - Laveran and Mesnil, 1912, comprehensive
monograph; for subsequent work see general texts and Tropical
Diseases Bulletin. : .
| LEISHMANIA ~ Closely related to the trypanosomes are cer-
tain minute intrscellular parasites of man and animals classed
under the genus Leishmania and often referred to in medical
literature as the Leishman-Donovan bodies. They produce two
types of disease - the one generalized, or systemic, and the
other cutaneous. The former is illustrated by a widely dis-—
tributed disease known as kala-azar or tropical splenomegaly,
and by various native names. The causative organism is
Leishmania donovani, the type of the genus.
Leishmania donovani occurs in cells of the spleen pulp,
bone marrow and lymphatic glands as a very small rounded or
slightly pear-shaped organism measuring 1-2” in diameter,
less than one-fourth that of a red blood coupuscle of man.
They were long supposed to be degeneration products but through
the discovery that they possessed a nucleus, a kinetoplast and
a small rod-like body in the cytoplasm the relationship to
trypanosomes was recognized. The correctness of this interpre-~-
tation was established by finding that the organisms could be ar-
tificially grown in blood media and that they then developed into
flagellate Herpetomonas forms, very similar to those found in the
intestine of various insects. It has been suggested that the
leishmaniases of man are transferred by the bed-bug or by sand-
flies of the genus Phlebotomus but no satisfactory evidence has
yet been adduced. That the parasites are transmitted by some
arthropod is most probable,
The cutaneous type of leishmaniasis known as "tropical sore”,
"Delhi boil" and by various other local names, is an ulcerating
160834:
infection of the skin widely prevalent in warm countries of a]
both the Old and New World. ‘The causative organism is L. eee
tropica, a parasite littie distiaguishabie from L. donovani.
Tn this ceaee, too, the method of trensfer is vnknown thoven
there seems more reason to believe that the vectors are sand-
flies of the genus Phlevotomus.
References. - Laveran, 1917, comprehensive; Wenyon, 1922,
review; Young and Hertig, 1926, Indian Journal of Medical ~
Research, and Tropical Disease Bulletin for experimental
studies.
TRICHOMONAS HOMINIS. (T. intestinalis). - The genus
Trichomonas contains numerous species infecting cold and warm~-
Slooded animals. There are usually recognized three species
occurring in man. Of these the best-known is the common
intestinal form, T. hominis.
Description. ~ Trichomonas hominis is a pear-shaped
organism 7 - 15 in léngth by 7 - 10” in breadth. A spherical
nucleus is near the anterior end and close to this @ «
blepharoplast from which arise three long, forward directed,
free flagella; and a fourth directed posteriorly and connected
with the body by an undulating membrane. &xtending from the
anterior end and projecting candad is a hyaline, non-staining
rod known as the axostyle. The function of this rod is
problematic but it is generally regarded as a supporting
structure. At the base of the flagella is a slit-like mouth,
or cytostome, through which bacteria and, occasionally, blood
corpuscles are ingested.
Reproduction. - Longitudinal fission of the trophozoite is
the only known form of reproduction. The supposed cysts, often
figured, are plant organisms belonging to the genus Blastocystis.
Prevalence. <- While this species is often referred. to as
the commonest intestinal flagellate of man there are no definite
data to warrant this designation.
Pathogenicity. - The available evidence indicates that
Trichomonas hominis is non=pathogenic. However it should be
noted that Kessel, 1926, produced a fatal diarrhoea in kittens
experimentally infected with this species.
Method of infection. - Since no cystic stage is known,
is difficult to explain the method of transfer of this parasite.
The experiments of Hegner, 1926 a, and of Kessel, 1926, in-
A@icate that infection may be directly from the trophozoites.
1608
De eeoo
RELATED SPECIES. - Similar flagellates of the genus
Trichomonas occur in the mouth and in the vagina and are
Separated by some workers as distinct species, T. elongata
and T,. vaginalis. Other species are common in the caeca of
other mammals, birds, reptiles aud amphibians. One of the
largest and most available for study is Trichomonas augusta
(Tetratrichomonas) which occurs in the intestine of frogs,
toads and salamanders.
References. - Bensen, 1909, human forms; Dobell, 1909,
protozoa of frogs; Kessel, 1926, transfer of T. hominis to
kittens; Kofoid and Swezy, 1915, reproduction; Wenrich, 1921,
rodent species.
CHILOMASTIX MESNILI. - This flagellate which likewise in-
habits the large intestine and caecum of man, resembles
Trichomonas hominis and is frequently mistaken for it, on
hurried examination. It has three anteriorly directed flagellum
and a large cytostomal cleft, within which is a fourth flagellum.
It may be readily distinguished from Trichomonas by the lack of
the axostyle and the undulating membrane. The living organisms
exhibit an active, jerky movement as contrasted with the slow-
er rotatory movement of Trichomonas. They vary considerably in
size, Hegner and Taliaferro stating that "average-sized specimens
are from 8 to 14 microns long, others are smaller, and some reach
a length of 24 microns. The width is from one-half to one-
fourth the total length".
Reproduction. - The trophozoite reproduces by longitudinal
fission. Lemon-shaped cysts measuring from 7 - 10M by 4 - 6 At
are also formed and within these mitotic divisions occur. Care
must be exercised to avoid confusion of the cysts with
intestinal yeasts.
Pathogenicity. - There is no evidence that C. mesnili is
injvrious to itS human host. It is apparently about a8 common
as ig Trichomonas hominis. Related forms are found in the
guinea pig and in a number of other vertebrates.
References. - Kofoid and Swezy, 1920, morphology; Leiva,
1921, C. intestinalis from guinea pig; Swellengrebel, 1917,
cyst formation.
GIARDIA LAMBLIA (Lamblia intestinalis, Giardia intestinalis ).
This is a fairly common parasite of the small intestine, duodenum
and gall bladder of man. Historically, it is of special interest
as being the first protozoal parasite noted for man.
Description. - In shape Giardia intestinalis resembies half
of a longitudinally split pear, the terminal portion being
1608oF
Prophylaxis. « The chief measures for protection against
this parasite are proper sewage dispos al and the same general
precautions as those against amoebic infections.
RELATED SPECIES. - A considerable number of spe cies Ciardia
have been described, chiefly infesting mammals. “In general they
clos aly resemble each other and those of man gut most workers
consider that those of man are not transmissible to animals.
Of the described species may be mentioned: - Giardia muris
(Grassi 1879) which is found in mice, wild pats and white rats
G. duodenalis Da avaine, 1875) in rabbits, G. canis Hegner, 1922,
G. eee ee ene 1925 and G. agilis Kunstler, 1ese. The
‘Tastementioned is found in tadpoles but disappears at time of
fecckor phosis. It differs Pao typical members of the genus in
being much more elongate and slender, the ratio of pody. “length to
breadth averaging 4.4.
References. ~ Dobell, 1920, Loeuwenhoek's discovery; Fantham
and Porter, I9I6, pathogenicity "and sunposed successful transfer
of G. lambia; Hegner, jgee2 comparative studies: Simon, 1921,
detailed study of G. lanbia ("onterica’), 1922, critique of
experimental work.
Class
tw
INFUS ORTA
The INFUSORIA are Protozoa of definite form, whose locomo-
tory apparatus is consti ituted by a more or less considera able
number of vibratile cilia on the surface of the body and which
typically possess two forms of nuclei, ~ a vegetative macronucleus
and a reproductive micronucleus. In the sub-class Suctoria Gilia
are present only during the young stages the adults ob being sessile
and in the sub-class Opalinata the two or more nuclei present
are of a single type.
Dependent on the distribution of the cilia on the surface
of the body four orders of the sub-class CILTATA are generally
recognized. ae
1. - Order HOLOTRICHA, in which the cilia are distributed
more or less evenly over the body.
2. - Order HETEROTRICHA have around the mouth a conspicu-
ous aboral zone formed by large cilia or vibratile membranes.
They are usually of swimming habit.
3. - Order HYPOTRICHA typically of creeping habit, the
dorsal cilia absent and those of the ventral surface often
modified to form prominent cirri.
4, - Order PERITRICGHA, whose cilia sre reduced to an
aboral zone.
Since there is only one important infusorian parasite of
man - Balantidium coli - the Monier eh of the class from a
1608
idan ia =
ptos ocean tees
a
Prophy ian. “ bia chief measures for pam etan against
this parasite are proper sewage Oe ae and the same eeneral
se aeautt he as those ag saint amoeb? » infections.
RELATED SPECIES. - A considerable aumber of species Giardia
have been described, chiefly infesting mammals. In ge eneral they
closely resemble each other and those of man put most workers
consider that those of man are not tra asmissible to animals.
Of the described species may be mentioned: - Giardia muris
(Grassi 1879) which is found in mice, wild pats and. white rats,
G. duodenalis (Davaine, 1875) in rabbits, G. canis Hegner, 1922,
eee
@, Gati Deschiens, 1925 and G. agilis Kuns sEler, L882. The
Tast-mentioned is found in tadpoles but disappears at time of
metamorphosis. It differs from typical members of the genus in
being much more ae Pe and slender, the ratio of body. “Length to
breadth averaging 4
References. ~ Dobell, 1920, Loeuwenhoek's discovery; Fantham
and Porter, I9I6, pathogenicity and supposed successful transfer
of G. lambia; legner , 1922, compara tive studies; Simon, 19el,
detaile dq study of G. lambia ("onterica’), 1922, aeieas of
experimental work.
Class INFUSORIA
The INFUSORIA are Protozoa of definite form, whose Locomo~
tory apparatus is cons stituted by a more or less considerable
number of tet Labia cilia on the surface of the body and which
typically posse two forms of nuclei, ~ a vegetative macronucleus
and a reproductive micronucle us. In the sub-class Suctoria Gi118.
are present only during the young stages the adults “being sessile
and in the sub-class Opalinata the two or more nuclei oresent
are of a single typo.
Dependent on the Aistribution of the Gilia on the surface
of the body four orders of the sub-class CILTATA are generally
recognized.
1. - Order HOLOTRICHA, in which the cilia are distributed
more or less evenly over the bod;
2, « Order HEPEROTRICHA have " around the mouth a conspicu-
ous atoral zone formed by large ciiia or vibratile membranes.
They are usually of swimming habit.
3. - Order HYPOTRICHA typically of creeping habit, the
dorsal cilia absent and those of the ventral surface often
modified to form prominent cirri.
4. ~ Order PERITRICHA, whose cilia sre reduced to an
aboral zone.
Since there is only one important infusorian parasite or
man - Balantidium coli - the significance of the class from a
160858
parasitological viewpoint is usually overlooked. In reality,
all of the orders contain parasitic species, some of them ex~
hibiting extraordinary modifications in form and piological
adaptations.
The simplest of the INFUSORIA are the holotrichous
Opalinata which are parasitic in the intestine of frogs and
Other amphibia. They possess two or more nuclei which are all
of one type. They exhibit a sexual reproduction characterized
by the complete fusion of uninucleated gametes. Since represen=
tatives of this group from our common frogs are always available
for study, we shall consider briefly the best known form,
Opalina ranarumn.
OPALINA RANARUM is an European form found in the rectum of
frogs, toads and a salamander. They are so large that they may
be seen with the naked eye as whitish specks in the fecal mass.
Structure. - The flattened, oval body is covered by fine
cilia which are arranged longitudinally in parallel rows, giving
a striate appearance to the organism. There is no trace of a
cytostome or other opening. The granular endoplasm contains
numerous nuclei which are uniformly distributed and which
multiply by mitotic division as the organism grows.
Reproduction. - During the greater part of the year
multiplication occurs by an oblique division into two parts,
each of which is multinucleate. In the spring of the year there
occur many rapidly succeeding divisions which finally result in
the production of small individuals, 40 - 50/% in length, which
contain only a few nuclei. These surround themselves with cysts,
measuring 30 - 70M which, passing out with the feces are taken
up by tadpoles. From the cysts emerge the enclosed multinucleate
ciliates which divide repeatedly and give rise to the small
uninucleate gametes. These gametes fuse in pairs and again a
eyst is formed, which is presumably taken up by a second tadpole
before the young Opalina emerges. When this occurs the large
multinucleate forms are produced by growth and nuclear division
without accompanying division of the cytoplasm.
Related forms. - Metcalf, 1923, recognizes some 140 species
and a number of sub-species of Opalinata. Of special interest
ig Proto-opalina intestinalis which is only binucleate in the
mature Stage. The common species of Opalina in our native Rana
pipiens is 0. obtrigonoidea.
References. - Konsuloff, 1922, reproduction; Metcalf, 1909,
anatomy and reproduction, 19235, anatony and reproduction of Prota-
opalina, monographic treatment of group.
L608
eeeehe
BALANTIDIUM COLI. - This important ciliate of man occurs
also in the pig and is transmissible to monkeys.
ii lta li
Description. - Balantidium coli is a_ large oval pear-
shaped organism, measuring 300 - 200 in length by 20 - 70%
in breadth (Brumpt). At the anterior end is a slit-like
cytostome, or mouth, bordered by the coarse aboral cilia. The
remainder of the body is covered by rows of uniform cilia.
There are two contractile vacuoles and at the posterior end an
anal aperature. The macronucleus is a kidney-shaped body near
the center, the micronucleus minute and lying in the depression
of the larger one,
Reproduction. - Asexual reproduction is by transverse divi-~
sion. A form of sexual reproduction occurs in which two individ- |
uals become encysted and are believed to fuse. In addition
single individuals may become enclosed in a protective cyst |
wall 50 - 60 in diameter. In this condition they are dis- |
charged and give rise to new infections. |
Pathogenicity. - Balantidium coli is an active parasite,
which not infrequently vores into the submucose of the large
intestine and causes considerable ulceration. It is un- |
guestionably a cause of a specific diarrhoea but, like Endamoeba |
histolytica, it may be present without causing definite symptoms.
Geopraphic distribution. - This parasite is widely dis-
tributed. A number of cases have been reported for the United
States, Central America and Porto.Rico, as well as for the Old
World.
_ Methods of infection of man. - Infection is brought about
by the ingestion of the cysts. The experimental evidence indi-
cates that man may be infected by cysts from pigs as well as by
those from other humans.
References. ~ Brumpt, 1909, pathogenicity; Nisbet, 1920,
occurrence in the U. 8.3; Walker, 1913, experimental and
pathology.
RELATED SPECIES. - Balantidium minutum Schaudinn, 1899,
has been reported asaparasite of man ‘but is regarded by Brumpt
as a coprozoic form. Other species have been reported for
cattle, sheep and the guinea pig. Frogs and toads commonly
harbor B. entozoon and other species in the rectum and
numerous species have been described for invertebrates. of
these B. blattarum is frequently to be found in the American
cockroach. —
NYCTOTHERUS. - Infusoria of this genus are oval or kidney-
shaped organisms characterized by a straight, linear peristome
160840
along one border, leading to an oblique more or less curved
cytostome in the equatorial region. The macronucleus is almost
central and near it is the micronucleus. Three species have
been reported for man. but their parasitic nature is questioned.
Next to species of the genus Opalina the most common of the.
ciliates of amphibians are of this genus, N. cordiformis being
the best known. Other representatives of The genus are report-
ed for insects, myriapods and crustacea.
Glass SPOROZOA
| The class SPOROZOA is a somewhat heterogenous group of Pro~-
tozoa which are exclusively parasitic and which lack definite
locomotory organs, mouth, anus and contractile vacuoles. They
produce at some stage in their life history resistant spores
which are not, however, the infective forms, but which give
rise to sporozoites which are the forms infecting new hosts.
The class is commonly divided into two sub-classes - the
TELOSPORIDIA and the NEOSPORIDIA. In the Telosporidia the ~
sexual reproduction, or sporogony occurs in the adult organism,
when the period of growth is completed. In the Neosporidia,
on the contrary, sporogony occurs during the period of growth.
The forms of chief medical interest are classed in three
orders, the COCCIDIIDA, the HAEMOSPORIDIA, and SARCOSPORIDIA.
Three other orders - the GREGARINIDA, the MYXOSPORIDIA and the
MICROSPORIDIA contain forms of much zoological interest, as well
as of considerable economic importance. We shall consider
typical forms of these six orders. :
order GREGARINIDA
The GREGARINIDA are coelom-inhabiting Sparozoa reproducing
typically by spore formation alone, after the fertilizing union
of similar gametes. They are very common as parasites of .Inver~
tebrates, chiefly insects, but. the majority of species are
probably harmless to their hosts. Dissemination is usually
passive, infection being by way of the alimentary canal.
In spite of their relative unimportance as. parasites, the
generalized life cycle of the Gregarinida and their close rela-
tionship to important groups of mammalian and human parasites
makes them important objects of study. One of the most widely
distributed and best known species is Monocystis agilis.
MONOCYSTIS AGILIS - This parasite is found in the seminal
vesicles of the earthworm, Lumbricus terrestris. In most
regions where this species Of earthworm is common the majority
of individuals are infected. If a specimen is pinned out with
160841
the dorsal side uppermost and opened by a longitudinal slit
anterior to the clitellum, the three pairs of cream-colored
seminal vesicles project from the 10th, lith and 12th
segments. If a portion of one of these is removed with forceps
and tapped in a drop of water on a slide various stages of the
parasite may be found among the brush-like groups of spermatozoa
and the spherical sperm morula.
Description. - The earliest known stage is a minute
nucleated stage, known as the trophozoite or vegetative stage,
which lives among the cells of a sperm morula, and grows at the
expense of the developing sperm cells. The body is somewhat
spindle-shaped and differs from that of many Gregarinida in
that it is not divided by a transverse partition, The endoplasm
is coarsely granular and contains a single nucleus. After a
time the trophozoite enters the seminal fluid and in this stage
may move about by a slow gliding movement.
Reproduction. - Reproduction is by spore formation only.
Two similar individuals, now known as gametocytes, come to-
gether without any fusion and form about themselves a two
layered cyst wall. Their nuclei divide repeatedly and the
daughter nuclei migrate to the periphery of their respective
cells and with rounded masses of protoplasm are separated from
the remaining cell body, or residual protoplasm, as gametes,
The gametes now unite in pairs to form zygotes. Their nuclei
fuse and a boat-shaped sporoblast is formed which by the
secretion of a hard cyst wall becomes a spore. Finally the spore
nucleus and protoplasm divide to form eight sporozoites, or in-
fective bodies.
Dissemination. - By the death and breaking down of the host
or more commonly by its being taken by birds the cysts contain-
ing hundreds of spores with their sporozoites are widely dis-
seminated. Infection of new hosts probably takes place by in-
gestion of these cysts and liberation of the sporozoites in the
alimentary tract.
References. « Cuenot, 1901; Hesse, 1909.
RELATED SPECIES. - A number of other species of wnocystis
from the seminal vesicles of carthworms have been described, but
their separation is difficult except in the trophozoite stage.
Our local small earthworms, Helodrilus caliginosus, are very
commonly infected by gregarines of the genus Zygocystis. In
this genus two or three trophozoites are usually intimately
associated as a compound organism though solitary forms are
sometimes present. The developmental stages are similar to those
of Monocystis. For a brief discussion of Zysocystis cometa
see Mickel, 1925.
160842
Favorite sources of laboratory material illustrative of Gre-
garinida are grasshoppers, cockroaches and especially "meal-
worms", the larvae of the beetle Tenebrio molitor. Valuable aids
to the study of the group are the two monographs by Watson,
1916, (Watson) Kamm, 192.
Order COCCIDIIDA
The Coccidiida are cell-infesting Sporozoa which typically
reproduce intracellularly by asexual spore formation (schizogony),
as well as by true sporogony, thus giving a life-cycle with an
alternation of asextal and sexual generations. The former
provides for the multiplication of the parasite within the in-
fected host while through sporogony the infection of new hosts
is brought about. After fertilization the oosphere forms
sporoblasts which may or may not be covered by a sporocyst mem-
brane, and which may each become transformed into one or several
sporozoites. The chief differences between the Coccidiida and
the typical Gregarinida are, then, the intracellular habitat of
the parasites and the interpolation of an asexual cycle.
A readily available species for the study of the Life cycle
of a coccidian is Eimeria stiedac.
EIMERIA STIEDAE (Coccidium oviforme). - This liver-infest-
ing parasite is the causative organism of a very serious disease
~ coccidiosis ~ of rabbits. Its ravages are especially severe
among young tame rabbits.
Description. «- The parasite leaves the body of the host,
with Feces, in the oocyst stage. The oocysts are ellipsoidal
or ovoid somewhat yellowish bodies varying considerbly in size
(33 -~ 43 by 18 - 30”), with smooth, thick shells having a
micropylar-like depression at one pole, This gives them some-
what the appearance of fluke eggs and they have been frequently
mistaken for such. The granular protoplasmic content is at
first distributed uniformly but soon becomes collected into a
spherical mass.
Development. ~ In the presence of moisture and summer
temperatures the oocyst becomes mature in three or four days.
The nucleus and protoplasm divide to form four sporoblasts and
around each of these there is formed a cyst wall, transforming
them into ovoid sporocysts. By division each of these forms
two sporozoites, and a smail mass of residual protoplasm. ‘The
cocysts are now in the infective stage. If taken up by a new
host the sporozoites escape from the spores, make their way
through the micropyle of the oocyst and enter the cells of
the bile ducts. Here they become the rounded schizonts, which
ultimately divide into 6 - 30 (Wenyon) asexualӎlements known
1608
PEE bers 98 cnmecne tenerPE bers A crecme tr
43
as merozoites. At a certain stage in the cycle there are pro-
duced the gametocytes. Unlike those of the Gregarinida, these
gametocytes differ in appearance and give rise to strikingly
dissimilar gametes. The female cell, or macrogametocyte is
distinguishable through its coarsely granular protoplasm,
rich in reserve material, while the microgametocyte pos-
gesses a clear, more or less fibrous appearance and increases
considerably in sizco. The macrogametocyte, by a process of
extrusion of chromatin analogous to the formation of the polar
bodies of the mammalian egg becomes the mature macrogamete.
In the meantime the microgametocyte has given rise to a large
number of minute microgametes, one of which enters the mature
macrogamete and fertilizes it. A firm resistant wall is
formed and the completed oocyst is discharged via the bile
ducts and intestine. ?
Intestinal Eimeria of the rabbit. - Not infrequently there
occurs an intestinal form of coccididsis of the rabbit which
may also result in fatal epizootics. This intestinal parasite
is often considered identical with that occurring in the liver,
but the present tendency is to regard it as a distinct species,
E. perforans.
Reported human infections. ~ There have been reported
several Gases of human infections by Eimeria stiedae and it
has been stated that these were especially to be met with in
men who cared for rabbits. The evidence in support of these
reports is very meager and it is possible thet they are based
on misidentification.
References. - Metzner, 1903; Perard, 1924; Wasielewski,
1904.
RELATED SPECIES. - Three species of Eimeria, - E. wenyonli,
B, oxysvora and E. snijdersi, have been described as parasites
Sf man but have been shown by Thompson and Robertson, 1926, to
have been based on the finding in human feces of cysts of two
species of coccidia of herring which had been accidentally
ingested. They afford a striking illustration of one source
of error in the determination of cysts or eggs from the human.
intestine.
In addition, a number of important BFimerias of domesti-~
cated animals are known. Of these may be mentioned: Eimeria
giirnii which causes a serious and often fatal disease o
cattie, E. diebliecki, in pigs in this country and the West
Indies, as well as in Europe. Eimeria avium a very common
parasite of chickens, turkeys, geese and other fowls which in
the case of young birds often causes serious epidemics.
16084.4
ISOSPORA SPECIES. - The genus Isospora is characterized
by the fact that the mature oocyst contains two spores, each
with four sporozcites. The best known forms are commonly
present in cats and dogs, and domesticated foxes are not in-
frequently infected by what are probably the same species.
Tsospora hominis and Isovora belli have been reported for man.
The latter Species, which is apparently the more common has
been separated by Wenyon on the basis of its smaller size, It
has sporocysts measuring 12 to 14 by 7 - 9M , each containing
four sporozoites and a large spherical residual body. Connal,
1922, cited by Wenyon, had an unusual opvortunity to note the
time of development and the pathogenicity of tnis species in a
laboratory worker who had accidentally ingested mature oocysts.
"Six days leter diarrhaea with abdominal discomfort set in.
This persisted for four weeks, and oocysts were discovered in
the stool three weeks after the onset of symptoms and were
present more or less continuously for twelve days after which
they were not found. The stools had become normal again and
recovery was complete",
References. - Connal, 1922; Dobell, 1919, 1926; Hall and
Wigdor, ISIS; Wenyon, 1923, 1926.
Order HAEMOSPORIDIA
The order Hacmosporidia includes the blood~dwelling
sporozoa, intracorpuscular, or free in the blood plasma, and
with or without alternation of hosts. The group is somewhat
heterogeneous. From the zoological viewpoint as well as from
the viewpoint of human pathology the most important are the
malarial parasites, belonging to the genus Plasmodium. It is
generally considered that there are three speciés infecting |
man « P. vivax, P. malariae and P. falciparum. A very closely
related form which has served much in experimental studies is
Plasmodium praecox of sparrows and finches.
PLASMODIUM VIVAX. - This is the cause of benign tertian
malaria of man, the most common type in this country.
Development. - The sporozoites are minute slender bodies
which are introduced into the circulation of man by the bite
of infected mosquitoes. Once in the blood stream they bore
their way into the erythrocytes, or red blood corpuscles, and
appear as the "signet-ring" stage characterized by a large un-
stained space in the center of the body.
This feeding form, or trophozoite, develops as a schizont
with granules of 4 characteristic black pigment - haemozdin -
in its protoplasm. The nucleus divides and by the end of the
43 hour period after infection the host cell ruptures liberat-
ing 12 - 25.asexual merozoites. These reenter red cells and
1608na
45
continue the asexual cycle.
Under certain imperfectly understood conditions some of the
young trophozoites develop as male and female gametocytes. In
the case of P. vivax these are round or slightly oval and being
larger than the réd cell cause it to become enlarged. These
gametocytes are capable of further develonvment only if taken up
by mosquitoes of the genus Anopheles. Under such conditions the
macrogametocyte undergoes a process of maturation similar to
that exhibited by a coccidian. The microganetocyte, however,
pecomes rounded and rapidly produces its gametes in the form of
flagella-like structures surrounding « mass of residual
protoplasm. This process, known as exflagellation rarely occurs
in the vertebrate host but typically in the stomach of the —
mosquito. Here one of the microgametes gains entrance into the
mature macrogamete and there results a motile zygote known as an
ookinete. -This bores through the wall of the stomach of the
mosquito where it settles down as an oocyst, without a firm cyst
wall, but capable of considerable further growth in size. Its
nucleus divides into a large number and about these the proto-
plasm becomes aggregated to form naked sporoblasts. The
sporozoites are formed directly, without a resistant sporocyst,
and escape into the body fluids of the insect. Through this
they make their way to the salivary glands thence to be inocula -
tea and continue the cycle in man when the mosquito feeds.
Periods of inoculation. = In man clinical symptoms of
malaria manifest themselves in about two weeks after an inocula-
tion by the mosquito. Multiplication in the blood of man is
rapid and Ross estimates that 150,000,000 parasites must be prea -
ent in the blood to cause clinical symptoms. The developmental
cycle in the mosquito requires from 10 - 14 days, but this period
may be considerably extended by cool weather,
Relation of the cycle of the parasite to clinical symptoms. -—
ro
Plasmodium vivax causes in man the relatively benign tertian
Malaria, in Which the acute attacks of fever occur every 48
hours. These attacks are correlated with the liberation of the
merozoites and their toxins into the peripheral blood. It
should be noted that multiple infections may occur and that if
infected mosquitoes bite on successive days the fever may occur
daily.
Latent malaria. - Infections of tertian malaria may persist
without clinical symptoms for three or four years after the ~~
patient has left a malarious district but on exposure to cold
or fatigue the disease may again become active. This so-called
‘Latent malaria is in all probability due to a great reduction
of number of the ordinary parasites in the blood rather than to
any peculiarity of life cycle.
160846
Prenatal infections. - As might be inferred from the—
nature oF the Malerial parasite it is possible for infections
to pass in the circulation of the mother to a foetus in utero.
Several undoubted cases of this nature are on record, al-
though there is no evidence that the oceurrence is a common one.
Malarial control. - The ultimate goal of malarial control
measures is the extermination of those species of Anopheles |
mosquitoes which have been found to act as hosts and dissemina~
tors of the parasites. In this country the U. S Public Health
Service has done especially noteworthy work along this line.
Since immediate mosquito control is not often feasible, measures
to avoid anophelines, such as choice of locality, the least
possible exposure in the evening, screening, and the use of bed
nets are essential in a malarious region. The sterilization of
the blood of patients by an extended treatment with quinine has
been shown by Bass, 1919, to be an efficient measure.
OTHER SPECIES OF PLASMODIUM OF MAN. - Plasmodium malariae
is the cause of guartan malaria in which schizogony requires
72 hours or, in other terms, the acute attack of the disease
is every fourth day. The developing trophozoites are more
angular than those of P. vivax and the adult parasite does not
cause enlargement of the rea corpuscle. The merozoites are
few in number, averaging 8 or G-
Plasmodium falciparum (Laverania malariae) causes a much
more Yntense and frequently Fatal tertian or Subtertian fever.
Only the early signet ring forms and the gametocytes are found
in the peripheral blood, the schizogony typically taking place
in the internal organs and giving rise to a variable number
(8 «= 24) of merozoites. The gametocytes, which appear only
after a week or ten days of acute clinical symptoms, are of a
characteristic crescent shape.
References. - The general texts on protozoology, notably
those of Hegner and Taliaferro, and of Wenyon, give detailed
discussions of the life history of the malarial parasite.
Craig, 1926, gives special attention to the medical aspects.
For current work on malarial control in this country see Public
Health Reports issued by the U. 5. Public Health Service.
BIRD MALARIA. - Birds are infected by Plasmodium praecox
(Pp. relictum), a species very similar to those of human
malaria, It differs from the species infecting man in that it
is transmissible from bird to bird by the common culcicine
mosquitoes rather than by anophelines. Though apparently rare
in this country it has been found several times in English
sparrows and has been transferred through hundreds of genera-
tions in canaries. As bearing on the question of latent malaria
in man, it is significant to find that bird malaria may be
1608e
a7
transferred to healthy birds by inoculation of a previously
tnfected bird whose verigheral biood parasites had supposedly
disappeared months before.
A related genus of haemosporidia is Haemoproteus
(Halteridium) a form much more common in birds in this country
than in Plasmodium preecox. The mature parasite is a large
horse-shoe shaped organism partially enclosing the nucleus of
the red blood cell rather than pushing it aside as does
Plasmodium. In some parts of this country a species of
Taemoproteus occurs in over fifty per cent. of the crows. It
is of special interest because it was through the studies of
MacCallum, 1898, on this form that the true significance of ex-
flagellation in human malaria was discovered. The best known
species is Haemoproteus columbae which is a parasite of the
common pigeon in many parts of the world and which undergoes
its sexual development in the parasitic fly Lynchia maura.
References. ~ Adie, 1915, 1924 development of Haemoproteus;
Ben-Harel, 1925, P. praecox; Taliaferro, 1925, infection and
resistance in P. praecox; Whitmore, 1918, Hartman, 1028; Huff,
1928. 3 ome
PTROPLASMIDAE
Piroplasmidae are minute hacmosporidians which inhabit the
rei blood corpuscles of various mammals but which do not form
the pigment (haemozoin) which is characteristic of the malarial
parasites. They undergo an essential part of their cycle in
ticks and are tranemitted by them to their mammalian hosts.
The Piroplasmidase are widely distributed, especially in tropical
and subtropical regions and are the cause of some of the most
devastating diseazes of animals. The first of these to be
studied in detail was Piroplasma bigeminum.
PIROPLASMA BIGEMINUM (Babesia bovis). - This is the cause of
a highly fatal disease of cattle, known in this country as "Texas
fever", but widely distributed and more generally known as "red-
water" from the fact that one of the symptoms of the disease is
bloody urine.
Descrivtion. - The organisms appear in fresh preparations
as minute pale pear-shaped spots, usually two in a corpuscle.
They vary in length from 2 - 4 and in greatest width from 1.5
~ 2a. The common appearance of two associated parasites is
‘due to dividing forms. They live at the expense of the red
corpuscles, as many as fifty per cent. of which may be infected
at one time. The characteristic bloody urine is due to break-
ing down of the corpuscles, the number of which may be reduced
to one-third or less. :
160848
Life cycle. + Piroplasma bigeminum is transferred from
animal to animal solely by cattlé ticks of the second genera-
tion. It is not the tick which has fed on the diseased animal
which transfers the infection but it is the progeny of such
ticks. In this country the tick concerned is the common cattle
tick of the South, Boophilus annulatus (Margaropus annulatus).
By analogy, it has been assumed by some that this cycle was a
sexual one but there is no satisfactory evidence that such
exists,
Methods of control. ~ Knowing the method of transfer of
Texas fever, 1ts control becomes primarily a problem in
economic entomology - the protection of cattle from the tick
and the extermination of the tick. Working on this basis the
federal Bureau of Animal Industry promptly established a
quarantine to prevent the movement of cattle from tick-infect-~
ed areas, and undertook active measures against ticks in these
areas. Through this work, considerable regions have been freed
from ticks and released from quarantine.
References. - Brumpt, 1920, development; Nuttall, 1915,
helpful discussion of piroplasmoses; Smith and Kilbourns, 1895,
of great historic and ecconomic interest, as first demonstration
of arthropod transmission of disease.
Order SARCOSPORIDIA
Sarcosporidia are Sporozoa parasitic in the muscle of
vertebrates, particularly mammals, although they have also been
recorded for birds and reptiles, They very rarely occur in man
but are common in sheep, pigs, cattle and horses, appearing as
whitish elongate. ovoid bodies often clearly visible to the
naked eye. The best-known form is Sarcocystis tenella from the
sheep. It is transmissible, by feeding, to mice, and Hartmann
' recommends that material for study be obtained in this manner,
allowing two to three months for development.
‘SARCOCYSTIS TENELLA. « The ovoid cysts in the muscle of
the sheep attain a length of some 20 mm. (4/5 of an inch). The
capsule is of two layers - an outer strongly staining layer
showing radial striation, and an inner layer which projects
into the cyst, dividing it into chambers. The outermost of
these chambers are filled with a number of rounded cells, 4 ~-
7/4 in diameter, which are known as pansporoblasts. Towards the
center the chambers are large and contain sickle-shaped spores,
or "Raineys corpuscles", while in old parasites the more central
spaces are empty except for obviously degenerating bodies.
1608
edepy
49
Development. - The knowledge of the life history of the
Sarcosporidia i8 very meager. When fed to mice the spore
membranes rupture and liberate amoeboid forms which enter the
intestinal epithelium. Here they multiply but soon disappear
from the intestine and the earliest stages known in the muscle
do not appear until nearly two months later. According to
Alexeieff, 1913, the cyst wall and the septa forming the
chambers are the product of the host cell, but this interpreta-
tion has been criticised.
Effect on the host. ~ Sarcosporidia may be present in con-
siderable numbers without apparent effect on the host. On the
other hand, infections are sometimes so intense as to obviously
cause mechanical injury if nothing more. Muscular paralysis
in pigs and horses has been attributed to Sarcosporidia but
without satisfactory cvidence. Various investigators have
succceded in extracting from the parasites a toxic substance
known as sarcocystin.
Method of transfer. - While several species of: Sarcocystis
have been shown to be experimentally transmissible by feeding
to rodents, it is puzzling to find that the most common forms
are in herbivorous animals, A plausible theory is that the
parasites occur in some form in insects which are accidentally
taken up by grazing animals, but extensive studies have failed
to verify this suggestion.
HUMAN INFECTIONS. «- There are some half dozen recorded
cases of infection of man by Sarcosporidia, but in none of them
were definite clinical symptoms clearly traceable to the
presence of the parasites.
References. + Alexeicff, 1913, morphology and development;
Darling, I909, 1919, human infections; Erdmann, 1910, cxperimen-
tal feeding; Scott and OtRoke, 1920, consider that there is an
infective intestinal stage.
Order MYXOSPORIDIA
The Myxosporidia are parasites of cold-blooded vertebrates,
especially Known as causing scrious cpidemics among fish. They
occur in hollow organs such as the kidnoys, uriniferous tubules
and bladder or they may be tissue parasites in the skin, fins
and muscles, where they produce tumor-like swellings. They are
characterized by the fact that the trophozoite, or feeding stage,
is amoeboid and that spore formation commences at an early stage
and proceeds continually during the growth of the trophozoite.
The spores produced within the protoplasm of the trophozoite
are enclosed in a bivalve shell and possess two or, rarely, four
distinctive structures known as "polar capsules". These bodies -
160850
when stimulated extrude a long filament which serves to anchor
the spore while the infective element is entering the tissues
of its host.
References. - Gurley, 1894; Kudo, 1919; Thelohan, 1895;
Ward, I920.
Order MICROSPORIDIA
The Microsporidia are closely related to the Myxosporidia
Since they possess a polar capsule within which is coiled the
polar filament. The spores are minute, frequently less than
5/7 in length, and contain an exceedingly long filament. They ave
chiefly parasites of insects, although they occasionally infect
fish, The most noted form is Nosema bombycis.
. NOSEMA BOMBYCIS. - This is the cause of the famous pebrine
or silkworm discase which until the work of Balbiani and of
Pasteur, threatened to wipe out the silk industry of France.
Form. - The parasites occur in the tissues of the host,
including the ovaries, as minute amoeboid organisms which
multiply rapidly and become transformed into spores. These
Spores are oval, 3" long by 1.5 wide and contain the typical
‘polar capsule. Behind this at the posterior part of the spore
is the binucleate infective agent. When taken in by the silk-
worm this organism escapes, enters the intestinal epithelium
and finally fills the tissues of the body.
Development. ~ There are two methods of spread of the
disease. ‘The spores passing out with the excrement of the in-
fected larvae are scattered on leaves and taken up by other
caterpillars. Or, if a diseascd caterpillar succeeds in trans-
forming into a moth the parasites which have reached the ovaries
infect the eggs and from these are hatched weak, discased cater-
Pillars which, though they soon dic, have contaminated the food .
of. the colony.
Control. - As a result of his studics of silkworm disease |
Pasteur found that by microscopic examination of the tissues of
the adult moths he could determine whether the infection was
‘present or not. Using only eggs from healthy individuals ho
was able to produce healthy caterpillars and thus to reestablish
the silk industry of France on a profitable basis. Ina strik-
ing manner these methods have been applied in recent years by
Howard in China, ;
‘References. - Howard, 1925; Pasteur, 7870; Stempell,
1909, development.
1608ea
os iuemaet eee
SL
NOSEMA APIS. - Closely allied to N. bombycis is a parasite
very commonly found in the honey bee. By analogy, it has been
supposed to cause considerable mortality but evidence regarding
this is unsatisfactory. See Fantham and Porter, 1912; Hertig,
4925; White, 1919.
RICKETTSIA BODIES
Three important diseases of man, - typhus fever, trench
fever and Rocky Mountain spotted fever ~ which are carried by —
arthropods, are caused by very minute intracellular, bacterium-
like organisms known as Rickettsia bodies. Cowdry, 1926,
defines these as “gram negative, bacterium-like organisms of
small size, usually less than holf a micron in diameter, which
ere found intracellularly in arthropods, wnich may be more or
less pleomorphic and stain rather lightly with analin dyes, but
which resemble in most of their properties the type species,
R. prowazeki, the cause of typhus fever.
The name was first applied by Rocha Lima, 1916, to the
organisms in lice, in honor of Howard Taylor Ricketts who lost
his life in the course of his studies of typhus fever. Stimu-
lated by the finding of these bodies in the arthropod carriers of
the diseases mentioned and in the endothelial cells of the in-
fected humans, extensive studies of insects and their allies have
been made, and upwards of fifty species of "Rickettsias" have
been described, from almost as many different hosts. It is
Sienificant that a number of these are found in non-blood-sucking
insects, so that the earlier assumptions that they were all
pathogens of man or animals must be discarded. However, it is
quite possible that some of those found in plant-feeding insects
and mites may be the cause of diseases of plants.
Whether they are protozoa or bacteria is an unsettled
question,- some workers even regard them as merely cell granules.
Their chief interest to the animal parasitologist lies in their
host relationships and the evidence of their transfer from the
invertebrate to the vertebrate host.
References. - Cowdry, 1926; Hertig and Wolbach, 1924;
Wolbach, 1919; Wolbach, Todd and Paifrey, 1922.
Glass SPIROCHARTA
The Spirocheaetes are spiral organisms with flexible, slender
bodies, diffuse chromatin and active movements. There has been
much discussion as to whether they are bacteria or animals - a
futile discussion since classifications are man made, Of char-
acteristics usually regarded as protozoal, are their failure to
grow on ordinary bacterial media, their reactions to arsenicals,
1608yy
52
and, especially their complicated life cycle which in the best
known forms, is undergone in an invertebrate. As a type we may
consider Treponema recurrentis.
TREPONEMA RECURRENTIS (Spirecnaeta obermeiri). - This is
the cause of a relapsing fever of man, characterized by repeated
attacks lasting from three to five days, followed by a similar
interval of normal temperature. The organisms occur in the blood
as slender flexible spirals, averaging 15/* in length and not
more than 0.34 in width. Reproduction is by transverse fission.
Transmission from man to man is by the body louse. Taken up
by these insects the spirochaetes alter rapidly in the stomach
and appear to disappear completely. On the sixth day they may
be again observed but in the body cavity of the louse. They are
not transferred by the bite of the insect but by the crushing of
the infected louse and the active penetration of the spirochaetes
through the skin or their inoculetion by scratching.
Related forms. - Relapsing fevers caused by organisms which
are not morphologically distinct from T. recurrentis are widely
distributed and have been given different names. The typical
form is the European relapsing fever, but in North America, North
Africa and various other regions the similar parasite is trans-
mitted by the louse and is probably the same species. In West
Africa a very similar form is conveyed by the excrement of a
tick attacking man.
References. - Nicolle, Blaizot and Conseil, 1912, 1915;
Nicolle and Lébailly, 1920; Nuttall, 19le.
TREPONEMA PALLIDUM (Spirochaeta pallida). - The causative
organism of syphilis is an exceeainsily slender spirochaete which
differs from the above. in that it is transmitted by contact and
is a tissue-invading form. It measures, 5 - 15“ in length by
not more than .25-% in width. The spiral turns are about twelve
in number and quite regular. It is to be found in scrapings of
the primary and secondary lesions of syphilis but is difficult
to demonstrate in tertiary lesions. All of the tissues are in-
vaded, and especially heavily in prenatal infections. It is
transmissible experimentally to monkeys, dogs, cats, guinea pigs
and rabbits, and may be cultivated under strict anaerobic
conditions.
References. - Noguchi, 1911, cultivation; Schaudinn, 1907,
pioneer research.
160853
LEPTOSPIRA ICTEROHAEMORRHAGIAR, - This is the cause of a
peculiar cosmopolitan disease, known as Weil's disease, or
infectious jaundice. The organism resembles Treponema but may
be distinguished by its larger number of closely wound spirals.
Tt occurs not only in the blood but also in the urine and in
the tissues. The principal reservoirs in nature are rats which
are commonly found infected. The method of transfer is unknown
but it is believed that it may be conveyed through food contam-
inated by rats. Severe cases of Weil's disease closely resemble
yellow fever and the organism is of special interest because it
is now generally beliéved by students of the subject that
Leptospira icteroides, described by Noguchi, 1919, as the cause
of yéllow fever is in reality Leptospira icterohaemorrhagiae
rather than the long-sought organism of that disease. For a
valuable discussion of this question, and bibliography, see
oe: es in Annals of Tropical Medicine and Parasitology,
: £245 - 259.
References. - Ido, et al, 1916, prophylaxis; Neill, 1918,
infectious jaundice in the U. S.; Noguchi, 1917, in American
wild rats.
160854
T - REPRESENTATIVE PLATYHELMINTHES
Class TREMATODA
Important Generel References
In addition to the general text previously cited see
Benham, 1901; Braun, 1889-1895; Gamble, 1896; Looss, 1894, 1910;
Pratt, 1916; Ward, 1917; Ward and Whipple, 1918.
The TREMATODA, or flukes; are exclusively parasitic flat-
worms, often leaf-like in shape, without a covering of cilia in
the adult state. They possess a well developed alimentary canal
with but one opening, the mouth, at the cephalic end of the body.
Suckers are developed on the ventral surface and in the region
of the mouth, their position and structure being of much
systematic value. With rare exceptions (blood-flukes) tremato~
des are hermaphroditic. |
The class is divided into. two subclasses, the MON OGENEA
and the DIGENEA. As indicated by the names, the monogenetic—
flukes develop directly, on a single host, while the digenetic
forms require two or more host species for their development.
Sub-class MONOGENEA
The MONOGENEA are almost exclusively ectoparasitic. They
have more than two suckers and often possess, in addition,
attachment hooks. The eggs are few in number and usually only
a single one is developed at a time. Development is direct and
without change of host.
The monogenetic flukes are chiefly parasites on the skin
and gills of fish, or in the bladder of frogs and turtles. On
fish they may occur in enormous numbers and since they feed on
the epithelial cells and biood they are sometimes the cause of
severe injury and even death of their host. We shall note
briefly a few representative forms.
The best known life history is that of Polystomum
integerrimum as worked out by Zeller, 1872 = '76.
POLYSTOMUM INTEGERRIMUM lives in the bladder of frogs. A
related species is found in this region (Minnesota) in tree
frogs of the genus Hyla and a number of svecies are known to
occur in our native turtles, but their life histories have not
been studied in detail. For a systematic review of North
American forms see Stunkard, 1917.
i Description.-- The mature fluke is about 5 mm. long by 1-5
mn. wide, flattened, with four eye spots at the anterior end.
1608oe
a
55
The alimentary canal is bifurcate, the two branches being con-
nected by many cross canals. At the posterior end are six
suckers in a circle, with attachment hooks between them.
Life history. - The eggs are iaid in the water by protru-
gion Of the body of the worm through the urinary aperature of
the frog. About 1000 eggs are deposited in 10 days. After
about 6 weeks a free-swimming ciliated larva hatches, but
perishes if it does not meet a tadpole within 24 - 48 hours.
If fortunate, it attaches to the gills of the tadpole, loses its
cilia, and remains for 8 - 10 weeks, forming suckers from behind
forwards. When the tadpole transforms, the young fluke enters
the oesophagus, passes down the intestine and lodges in the
bladder of the frog. It is said to require three years to reach
maturity.
Diplozoon parodoxum. - This appropriately named fluke .is
worthy of mention On account of its remarkable structure. The
adult animal is x-shaped, being made up of two permanently
fused individuals. They live on the gills of minnows and dis-~-
charge eggs which give rise to minute ciliated larvae. If
these succeed in attaching to a minnow they develop into a
simple larval form long known independently under the generic
name Diporpa. These Diporpae develop and mature sexual organs
only by conjugation in pairs. The union is permanent, the two
individuals fusing at the point of contact and developing with-
in each complete sets of genitalia.
Gyrodactylus. ~ Flukes of the genus Gyrodactylus are
minute, less than 1 mm. in length with a slender, flattened
body. The anterior end is prolonged as a pair of conical tips
through which empty glands secreting an attachment fluid; the
posterior enlarged, disc-like, with two large central hooks
and 16 simple marginal hooklets. When these flukes occur in
large numbers on the skin and gills of fish they may cause
serious injury and death. Related forms on the gills of black
bass have been noted as causing heavy losses in New York.
Sub-class DIGENEA
The Digenea are exclusively endoparasites. They have not
more than two suckers and are without hooks. Development is by
an alternation of a bisexual with parthenogenetic generations
(alloiogenesis); the bisexual generation almost exclusively in
vertebrates, the parthenogenetic in invertebrates. (Note, how-
ever, that Aspidogaster conchicola which is common in fresh
water mussels, completes its development in these molluscs.
Other exceptions might be cited).
1608
I~ prssapticeensit
56
{
The interpretation of the complicated life history of the |
digenetic flukes has been a slow process, dating back to the '
very beginning of microscopy. On account of its great practi-
cal importance, the most fully studied has been Fasciola
hepatica, the liver fluke of the sheep. It will best serve
as an itilustration.
Fasciola hepatica. - (Distomum hepaticum). - The liver
fluke of sheep and other ruminants. ‘The adult is the cause
of "liver rot", an infection which has caused loss in all —
countries where sheep are grown. Fortunately it is established
only in limited areas in the United States, chiefly in Texas,
Florida, Washington and Oregon.
Structure. - The adult is a flat, unsegmented worm, en-
larged in front, measuring 3 - 6 cm. in length. There are two
suckers, one at the anterior end and the second about one-fifth
of the way caudad. The cuticle is covered with minute,
caudally directed spines. The digestive system is branched,
ramifying all through the body. The excretory system is also
much branched, with a mesal, main duct opening by a minute
pore at the caudal end. The reproductive system is.
hermaphroditic, with branched ovaries anterior to the paired,
much branched testes, and with very prominent laterally placed
yolk glands.
Life history. - The adult in the liver discharges its
eges which pass out by way of the gall ducts and the intestine.
The egg is characteristically capped, or operculate. When it
reaches water the ciliated embryo, or miracidium, escapes and
enters the pulmonary chamber of a snail of the g ».us Limnacus.
There it loses its cilia and transforms into a sac-like
sporocyst which from special germ cells produces one or more
generations of similar sporocysts. These next develop rediae,
characterized by a simple unbranched alimentary canal. The
rediae enter the liver and other organs of the snail, and pro-
duce internally the cercariae, tad-pole-like with a forked
alimentary canal. Boring out of the snail these cercariae
settle on vegetation, lose their tails and develop resistant
cysts within which they remain as metacercariae, until taken
up by grazing sheep. The larval fluke then escapes, passes
to the liver and matures.
Parasitism of man. - In man, Fasciola hepatica occurs only |
as an incidental parasite, usually in small numbers. Several
fatal cases are on record. According to Leuckart, natives of
Lebanon, who commonly eat raw goat liver, suffer from a peculiar
affection due to the attachment of adult flukes in the throat.
References. - Hall, 1912, distribution in U. S.; Sommer,
1880, anatomy; Thomas, 1885, development. |
1608 |57
Flukes Infecting the Liver
Clonorchis sinensis. - The most common of the flukes in-
fecting the liver of man belongs to this species. It 1s common
also in cats and dogs and is transferable to rabbits and
guinea pigs and rats.
Description. - The worms are relatively small, measuring
from 10 = 20 mm. by 2 - 4 mm. The second sucker is in the
anterior third of the body; the intestinal branches long and
simple, reaching the posterior end of the body... The ovary 15
situated about two-thirds of the way caudad and is followed —
by the two greatly branched testes. The coiled uterus anterior
to the ovary is filled with numerous small, ovoid, operculate
eggs, dark colored, measuring 26 - 3044x 15 - 17%.
Development. - The miracidia develop in snails of the genus
Bythinia, the cercariae attaining full development in three
weeks. The metacercariae occur in at least 13 species of fish.
When ingested by man or other appropriate hosts they mature in
e6 days.
Distribution and incidence. - Clonorchis sinensis is wide-
spread in the Orient and not infrequently imported cases are
noted in the United States. It may occur in enormous numbers
in a single host and is apparently a long-lived species.
Watson, 1917, reports finding it at autopsy in Chinese in
Panama who had not been exposed to infection within the
preceding 20 years.
Reference. - Faust and Khaw, 1927, monograph; Kobayashi,
1915.
Opisthorchis felineus. - Flukes of the genus Opisthorchis
are closely related to those of Clonorchis but readily distin-
guished by the fact that the testés are compact and lobulated
rather than ramified. 0. felineus is widespread in Europe and
Asia as a parasite of the dog and cat and occasionally of man.
The metacercariae occur in the muscles of various fish.
Fed experimentally to dogs they mature in about 12 days.
A closely related species Opisthorchis pseudofelineus,
Ward, 1901, is fairly common in the liver of cats in this
country and makes a valuable species for study.
INTESTINAL FLUKES
About a dozen species of intestinal flukes have been re-
ported as occurring in man. Most of these are of rare occurrs
ence and apparently of little medical significance.
160858 '
The largest and best known is Fasciolopsis buski. |
Fasciolopsis buski. ~- This is a very common parasite of '
man and of the pig in India, China, Formosa and Indo-China.
It is the cause of considerable gastro-intestinal trouble in
man. Anemia results and, in severe infections, emaciation.
Description. - The worm is large and leaf-like, measuring |
up to 7 om. in length and about half as broad. The ventral
sucker which lies close to the anterior end, is very large, |
three to four times the size of the oral sucker. The twe-
branched testes lie mesad in the posterior half of the body.
The branched ovary and shell gland are about the middle of the
body. The large ovate eggs measure 120 - 130.4 x 77 - 80".
Life history. - The miracidia hatch within two to three
weeks after discharge of the eggs and undergo the typical
cycle in snails of the genera Planorbis and Segmentina. The
emerging cercariae encyst on the water chestnut and the water |
caltrop. Human infections result from the habit of cracking |
these nuts with the teeth. They mature in 90 days.
References. - Barlow, 1925; Nakagawa, 1922.
re HETEROPHYIDAR. - The family Heterophyidae is made up of a
number of very small flukes characterized anatomically by the |
fact that the genital pore is sucker~like and located at the
side of the ventral sucker. They are of medical and veterinary
interest because several species infect man, and the dog and
cat.
Of special interest is the fact that our native fish, as
well as those of Europe and Asia, are often bearers of the
encysted metacercariae. Locally, rock bass are especially
noted as having the minute, rounded black-pigmented cys ss in
the flesh and on the scales. Cuirea has published an import-
ant paper detailing his experiments with European species.
When the cysts were fed to dogs the flukes matured in 7 days.
In Formosa a closely related species, Metagonimus yokagawai,
encysting on the scales of fish, has been reported ag a
parasite of man. :
References. ~ Cuirea, 1924, for biological studies.
Ransom, 1920, has published a valuable synopsis of the family
with descriptions of new species from the fox, dog and cat.
Clinostomum in Fish and Frogs. - In this connection may be
mentioned another type of Tarval fluke often found in the
muscles of fish and in the mesenteries, imbedded under the
peritoneum of the body cavity, and in the lymph svaces between
160859 |
the skin and muscles of various parts of frogs. Cort, 1915,
who has studied these forms in detail, regards them as dis-
tinct spécies, C. marginatum in the fish, and ¢. attenuatum
in frogs.
The small, cream colored cysts, about the size of a grain
of wheat, or a little larger, are especially prevalent in
perch and in black bass. When abundant they attract the atten-
tion of fishermen who speak of the fish as "grubby". They have
been repeatedly mistaken for immature stages of the broad
tapeworm. Clinostomum marginatum matures in the mouth or the
throat of several different fish-eating birds, notably herons
and a stork. C. attenuatum has been reported from the American
bittern and the American herring gull.
References. - Cort, 1913; Osborn, 1911, 1912; Smallwood,
L914.
LUNG FLUKES
Man is subject to infection of the lungs by a fluke which
is very similar to, if not identical with, widespread species
occurring in the lungs of cats, dogs and pigs. FPollowing
Kobayashi, 1919, we shall consider them under one name.
PARAGONIMUS WESTERMANII. = The lung fluke of man is com-
mon in Japan, China, Formosa and the Philippines. Rarely,
imported cases have been noted in this country.
Description. - The mature fluke is around 12 mm. in length
and about a third as wide. It is almost round in cross-section.
The eggs are 85 = 100-'" x 50 - 67." ,.
Develonoment. - The intermediate hosts noted are snails of
the genus Melania. The cercariae escape and encyst in the flesh
of freshwater crabs and crayfish, with which they are taken up
by their definitive host. f
Effects on man. - This is one of the most dangerous of the
flukes attacking man. It causes a chronic cough and bleeding
from the lungs which is sometimes diagnosed as tuberculosis.
Sputum examination promptly reveals the eggs of the fluke.
Twenty-three cases of cerebral parasitism of man by this fluke
are on record. (Yokogawa and Suyemori, 1921).
References. ~ Ward and Hirsch, 1915; Kobayashi, 1919.
PARAGONIMUS KELLICOTTII. - Ward, 1908, has distinguished as
a separate species a lung fluke from cats and from hogs in this
country. In cats they have been noted as the cause of a
peculiar and persistent couch. The species has been reported
1608
:
|
|id
=
60
from cats in Nebraska, Minnesota, Wisconsin and from hogs in
Ohio. The writer has collected it from cats in Minnesota and
New York. The life history is unknown.
BLOOD FLUKES
The blood flukes of man, of which there are three im-
portant species, belong to the genus Schistosoma. In the older
literature the generic name Bilharzia is used. They are
characterized by the fact that they are bisexual and that the
two branches of the alimentary canal are united into a single
tube in the posterior fourth of the body. The male is the
larger and encloses the slender female in a ventral fold, the
gynaecophoric canal. The cercariae enter the human host
actively, through the skin.
Infection by these flukes is known as bilharziosis or
schistosomiasis. Until recent years it was attributed to a
Single species, Schistosoma haematobium.
SCHISTOSOMA HAEMATOBIUM. - This is the best known and the
most dangerous of the blood flukes of man. It is readily trans-
missible, experimentally, to monkeys, rats, mice and guinea pigs.
“Description. - The male is cylindric, 10 - 15 mm. in length
and not exceeding 1 mm. in breadth. The oral and ventral
suckers are close together. The alimentary canal bifurcates
just caudad of the ventral sucker but again fuses to form the
Single tube which extends through the posterior half of the worm.
The females are cylindrical and thread-like, slightly ex-
ceeding the males in length. The ovary is elongate-oval, and
lies anterior to the intestinal tube. ‘The yolk glands occupy
the posterior part of the body, laterad of the intestine. The
uterus is a long tube opening to the exterior by the genital
pore immediately caudad of the ventral sucker. It is filled
with large, characteristic oval eggs, measuring 160-" x 60-" ,
without a cap, and tipped by a short, sharp spine. The coupled
worms make their way to the finer veins, especially of the
‘bladder and the uterus, and the female alone then passes to the
minute branches where she deposits her eggs. The spines engage
the wall of the vessel and finally the eggs are forced through
into the perivenous tissue. They enclose a well developed
miracidium. As a rule they are discharged with the urine,
though they may also be found in the feces.
Development. - The ciliated embryos, or miracidia, are soon
killed by the undiluted urine, but in water they quickly escape
by the rupture of the shell and seek snails of the genus Bullinus.
L60861 b
Failing to find a host, they die within 36 hours. In the
appropriate snail they produce sporocysts and daughter
sporocysts. The latter migrate to the liver and the gonads and
there develop fork-tailed cercariae directly, without produc- a
tion of rediae. Escaping from the snail, these cercariae ac- —
tively enter the human host through the skin, reach the blood
vessels of the liver and attain sexual maturity in about 6
weeks.
Effects on the human host. - The cntering cercariae pro-
duce a marked itching and often a definite skin rash which may
persist for two days.
The chief symptoms are due to the movements of the eggs in
the mucous membrane of the bladder, where they may be present
in enormous numbers. The laceration of the blood vessels re-
sults in bloody urine and often acute pain on micturition. In
severe cases sooner or later inflammation of the bladder occurs.
Not uncommonly the ova undergo calcification and become the
nuclei for stones in the bladder wall or cavity.
Prophylaxis. - Avoidance of, or sterilization of infected
water supply is the obvious method of protection against this
parasite. Drinking, or bathing in infected water, or even
using it for shower baths may result in contracting the disease.
It has even been noted that there is danger in handling newly
caught fish, which may have the living cercariae on them.
References. ~ Leiver, 1915; Manson-Bahr and Fairley, 1920;
Manson's Tropical Diseases, 8th ed.
SCHISTOSOMA MANSONI. - For years the presence of large
lateral»«spined ova associated with the terminal-spined form
had been noted and attributed by most observers to abnormali-
ties. In course of time it became apparent that these eggs
were found only in feces and that they occurred not only in
the regions where Schistosoma haematobium was endemic but com-
monly in the West indies and parts of South America where the
haematobium was unknown. For the newly recognized form the
Ssvecies Schistosoma mansoni was established.
Schistosoma Mansoni is the cause of intestinal
schistosomiasis, giving rise to dysenteric symptoms, bloody
mucous, and at times polypoid growths in the bowel. The worms
closely resemble Schistosoma haematobium. They are found
chiefly in the branthes of the portal véin and in the mesenteric
veins. The eggs measure from 120 - 160. x 40 ~- 60M and are
distinguished by the sharp lateral spine.
1608
|
|
|62
The intermediate hosts are snails of the genus Planorbis.
The life history and methods of infection are similar to those
of Schistosoma haematobium.
SCHISTOSOMA JAPONICUM. - This species is the cause of a
serious and often fatal disease of man in China and Japan.
Endemic centers also occur in the Philippines. Infection is
characterized by great enlargement of the liver and spleen
and by intestinal disturbances, thickening of the walls, and
formation of ulcers and polypoid growths.
The worms are similar in general structure to the preced-
ing species. The eggs are smaller, measuring only 70 - 75"
x 45 = 55-4. They lack a spine but possess a rudimentary
lateral papilla. The life history of Schistosoma japonicum
is very similar to that of S. haematobium and was, indeed,
worked out as early as 1909 by Japanese investigators. The
intermediate hosts are the snails Blanfordia nosophora and
Oncomelania hupensis. An important Pactor in the possible
dissémination of the parasite is the resistance of the first
mentioned snail to dessication for as long as three months.
: S. japonicum occurs in cats, dogs and cattle, as well as
in man.
References. - Faust and Meleney, 1924, monographic account,
including detailed account of the earlier work on this species;
Cort, 1920, on resistance of the intermediate host.
Native species of blood flukes. - Blood flukes of the
family Schistosomidae are parasitic in the circulatory system
of birds as well as in man, cattle and the previously mentioned
hosts. In addition there is a considerable number of species
found in our native turtles and fish. These differ from the
blood flukes of man in being hermaphrodcitic instead of dioeci-
ous, and in various structural details. However, as Ward has
pointed out regarding those of the turtle, the material is
readily available and affords in this country opportunity for
laboratory studies of forms adapted to living in the vascular
system. The valuable studies of Stunkard, 1925, should be
consulted.
LARVAL FLUKES
With increasing knowledge of the adult flukes affecting
man there has been emphasized the importance of study of the
cercariae to be found in snails and of the metacercariae or
encysted larval forms in fish, batrachians, crustacea and other
aquatic organisms. While a considerable amount of attention
has been devoted to these stages by European workers, it is.
16085
oly very recently that the problems which they present have
interested American investigators.
This rich field has been opened up by the comprehensive
studies of Cort; 1915; Faust, 1917; Miller, 1926; under the
direction of Dr. H. B. Ward, and by the numerous briefer con-
tributions by them and their associates. They will prove of
great practical value in ultimately forming a basis for the
study of the life histories of many of the flukes infecting
domestic animals.
Class CESTODA
Important General References
Benham, 1901; Braun, 1894-1900; Gamble, 1896; Leuckart,
1886; Meggitt, 1926; Pratt, 1916; Stiles, 1906; Stiles and
Hassall, 1912; Southwell, 1925; Ward, 1923; Ward and Whipple,
1918; (for classification of fresh water forms).
The CESTODA, or tapeworms, are flat worms which have
typically the form of a ribbon, made up of a large number of
Segments, or proglottides. At one extremity is the organ of
attachment, the scolex, provided with suckers of varying form
. and number, and in some cases, with hooks. The body cavity is
ree lacking, as is also the digestive tract. Food is absorbed
directly through the integument.
Tapeworms were known to the ancients but down until very
modern times: the most diverse views were held as to their
nature and origin. Indeed, the present day conceptions as to
their life history and the relationships of the adult worms to
the cystic stages date back only to the introduction of the
experimental method by Klichenmeister, 1851. His successful
attempts to produce typical tapeworms in dogs which had been fed
cysts from the abdominal cavity of a rabbit, and in cats fed
on cysts from the mouse liver, opened up an entirely new field
and stimulated work which rapidly elucidated the life nistories
of the most important species.
With rare exceptions, the known life cycles of the cestodes
involve at least two hosts, of different species. Of these one
or more is essential to the development of the immature stages
and one harbors the adult. An exception is afforded by the rat
and mouse tapeworm, Hymenolepis nana, which is able to complete
its development in one and the same host. The life cycles of
a large and important series of tapeworms infesting cattle,
sheep and other herbivores are still a puzzle. It seems prob-
able that they require an intermediate host, such as an insect or
mollusc, which is accidently swallowed by the grazing animal.
1608eo
64
Considerable confusion still exists in the classification
of the Cestoda. This is due to the fact that zoologists, —
medical men and veterinarians have often been interested in-
dependently and have described species without knowledge of
other work in the field. In many cases specimens have been
described as new because found in another host, while it was
formerly the practice to describe as separate species the :
immature and the adult stage. A relic of this early zoologi-
cal viewpoint is the retention of such names as Cysticerus
cellulosae although it is now known that this is only the cystic
Stage of the pork tapeworm, Taenia solium.
The class CESTODA is divided into two sub-classes, the
Monozoa and the Merozoa.
MONOZOA
The most primitive of the Cestoda are grouped in the sub-
class Monozoa. They are unsegmented forms and are of special
interest as showing relationships to the Trematoda, or flukes.
Most of the described species infect fish. The larvae of some
of the better known forms occur in annelid worms of the
family Tubificidae.
MEROZOA
The typical tapeworms belong to the group Merozoa. We
shall use as a type Taenia saginata, the most common of the
large tapeworms infecting man. ,
TAENTA SAGINATA. - This is the beef tapeworm of man. The
adult lives only in the small intestine of the human host while
the immature stage is found primarily in the intermuscular
connective tissue of cattle.
Form and structure. - The body is ribbon-like, forming a
chain of many segments, with a total length of 4 - 12 meters.
The head, or scolex, is minute, (upwards of 2 mn.) somewhat
quadrangular, with four suckers but without attachment hooks.
The head is followed by a short, unsegmented neck, following
which is the trunk, or strobila, made up of a séries of
proglottides, which may attain 2000 in number.
The alimentary canal, circulatory and respiratory apparatus
are entirely lacking. The nervous system consists of two
longitudinal cords connected in the scolex and extending through-
out the body. A superficial network of fibers is connected with
these cords. The excretory system is composed of two longitudi-
nal canals on each side, the larger ventral one being connected
with its counterpart by a transverse canal in each segment.
160865
Opening into these collecting vessels is a superficial network
of fine cavillaries. :
Near the middle of one side of each proglottis is e@
slightly raised genital papilla, or pore. The tapeworms are
hermaphroditic, each segment as it matures bearing a set of
reproductive organs. As is often the case in hermaphroditic
animals, the male organs come to maturity before those of the
female. They consist of a great. number of rounded testes,
whose efferent ducts unite to form a vas deferens which, near
the genital pore, enters the cirrus or penis, surrounded by 4&
cirrus sac. The female organs consist of the paired ovaries
Whose oviducts connect on the one hand with the vagina, passing
to the genital pore, and on the other hand, with the tubular
uterus which occupies the mesal line of the proglottis. Near
the juncture of the oviducts with che uterus is the small‘ round-
ed Mehlis! gland, often called the shell gland, while the larger
transversely elongate yolk or vitelline gland lies near the
caudal margin of the proglottis. Ripe proglottides have the
sex organs atrophied, except the uterus, which is very greatly
enlarged and with its 15 - 30 dichotomous branchings occupies
the entire segment. It is filled with embryonated eggs, of
which it is estimated there are 50,000 or more in a single
proglottis. The terminal proglottides with their mass of eggs,
break from the strobila and pass off with the feces. In the
case of T. saginata, these are expelled singly and often
exhibit GonSiderable motility after they have left the host.
Life history. - The expelled proglottides break down and
the eggs containing the six-hooked embryo (hexacanth embryo, or
onchosphere) are scattered on the soil and vegetation, to be
Still further disseminated by dust, rains, on the feet of man
and animals and, to some extent, by flies and other insects.
When taken up by cattle with food the emoryonic membranes are
digested by the gastric juices and the liberated hexacanth embryo
bores by means of its hooks through the walls of the alimentary
canal, into the circulatory system, to be carried chiefly to .
the intermuscular connective tissue. Here a cyst is formed, the
embryonic hooklets are discarded and the scolex of the future
tapeworm is developed by invagination of the cyst wall. This
larval or asexual form is known as the bladderworm or cysticer~ .
cus, the infected meat being known vopularly as "measly". The
Cysticerci mature in from eight tc twenty weeks and then if
ingested in the living condition by man the nead is everted and
attaches to the alimentary canal of its new host, where it
develops into the mature tapeworm in about three weeks.
Geographic Distribution and Prevalence. ~- Taenia saginata
is a cosmopolitan species, occurring wherever beef is an impo> «
tart food of man. According to Leuctart, the Abyssinians,
160866
who eat the fresh and uncooked flesh of their cattle, are al-
most universally infected and even consider that without the
parasite they would be unhealthy. Brumpt states that in
France 99 per cent of the large tapeworms of man are IT.
-saginata. It is certainly the common Taenia of man in the
United States although the observations of the writer indicate
that in the Great Lakes region the large fish tapeworm,
Diphyllobothrium latum is the more common in man. The once.
held view that the pork tapeworm, Taenia solium was common in
this country was certainly due to ¢onfusion of that species
with T. saginata. Stiles states that of 500 tapeworms of man
examined by him from 1891 to 1895, 297 were T. saginata and none
were T, soOliume As a rule when infestations with either of these
species occur, only a single specimen is found, its presence ap-
parently having established an immunity against further infec-
tion.
As for the cysticerci, or immature stage, the Federal meat
inspection retains about 0.6 per cent of the carcasses of cattle
examined, or 1 in 166, because of this parasite. This indicates
that infections of humans by the adult worm are more common than
is ordinarily supposed by medical men.
Prophylaxis. - The obvious method of avoidance of infection
is the thorough cooking of veal or beef used as food. The cysts
ly are unable to survive more than three weeks after the slaughter
| of their host and Ransom, 1914, has shown that this period may
be reduced to six days if the carcass is kept at a temperature
not higher: than 15°F.
Taenia solium. - The pork tapeworm of man superficially
bears much resemblance to 7. saginata. Like the latter, the
adult is found in the smalI intestine of the human host, only.
The larval form is found prinarily in the intermuscular con-
nective tissue of hogs. Occasionally it is found in various
parts of the body of man, and it has been reported also for the
dog, cat, rat, and various other animals. These forms obviously
play no role in the dissemination of the parasite since they are
not used for human food and the cysticerci have no chance for
further development.
Form and structure.: Taenia solium differ from T. saginata
in size, since 1t rarely exceeds 4 meters in length and the
number’ of segments is 1000 or less. The head is smaller,
globular and in addition to the suckers, has an apical rostellun,
which bears a double row of attachment hooks or is "armed", in
contrast to the hookless or "unarmed" head of T. saginata. ‘The
terminal proglottides are frequently discharged as fragments of
a chain, rather than singly.
1608ye
a
67
Life history. - The embryos from the discharged proglotti-
des when taken up by a pig develop in three or four weeks and
may, persist in the host for a year or more. When the cysticerci
are taken by man they mature in about three months.
Autoinfection of man. - Contrary to the usual rule, the em-
bryos of Taenia Solium are capable of developing also in man if
taken from soiled fingers or with food or drink or if by re-
verse peristaltic movement of the alimentary canal they pass to
the stomach. Vosgien, 1911 (cited by Brumpt) has analyzed 807
cases of Cysticercosis and found that in 46 per cent. the
cysticerci were in the eye, in 41 per cent. in the nervous
system and in only 3.47 per cent. in the muscles, This apparent
distribution is doubtless due to the fact that such cases affect
ing the eye or nervous system would manifest themselves, while
cysts in the muscles would be overlooked.
Geographic distribution and prevalence. - The pork tapeworm
was formerly assumed to bé the large tapeworm of man but now
known to be very rare in the United States and, as might be ex-
pected, is abundant only in those regions where it is customary
to eat imperfectly cooked or raw pork, in the form of sausages
or otherwise. In the United States it constitutes less than one
per cent. of the large Taenias of man; Brumpt reports one per
cent. for Paris; in Southern Germany it is likewise rare, but
has been very common in northern and eastern Germany. Braun
points out that even in this section of Germany the incidence
has greatly decreased in recent years, due to education of the
public regarding dangers from trichina, and to meat inspection.
Available data indicate that it is not uncommon in Central
America.
Prophylaxis. - Avoidance of imperfectly cooked pork.
RELATED SPECIES. - The name Taenia was originally applied
to tapeworms in general and is stiIT loosely so used by some
medical texts. It is correctly applied to those species having
a scolex with 4 simple cup-shaped suckers, proglottides usually
longer than wide, genital pores alternating irregularly and
never on both sides of a segment, and with uterus in ripe
segments composed of a median tube and lateral branches.
The two species above described are the principal taenias
found in man but several others have been reported for the human
host. ° The following are a few of the common species infecting
animals. -
Taenia pisiformis (syn., T. serrata) is the common tapeworm
of hunting dogs, the cystic stage being found in the mesenteries
and body cavity. of rabbits. This species and the following are
of special interest because of being the forms first used by
Kiichenmeister 1851, in his classical experimental studies on..the
1608et
68
life history of the cestodes,
Taenia teniaeformis (T. crassicollis}), is a common tape-
worm Of cats, contracted from eating mice and rats which serve
as the intermediate host. In these rodents the cysticerci are
to be found in the liver, and dre noteworthy because of the
long worm-like form of the invaginated head. The adult worm
is armed with very large hooks and practically lacks a neck,
the segmentation beginning immediately behind the head.
Taenia ovis is a tapeworm of the dog whose cysticerci
develop in the Sheep. It is of interest because these mature
forms occur in about 2 percent of the sheep inspected in this
country, and have been mistaken for cysts of T. solium and the
infected mutton condemmed, The work of Ransom, T9I3, has shown
the true source of sheep "measles" and that the cysts are not
infective to man.
Genus HYMENOLEPIS
The genus HYMENOLEPIS is composed of small, filiform worms
with broad segments, genital pores on one side, a retractile ros-
tellum with or without hooks, usually three testes in a trans-
verse row in each segment, uterus sacelike, filling the ripe
segment. Included in this genus are a number of tapeworms of
mammals and birds. Two species are parasites of man.
HYMENOLEPIS NANA (Taenia murina, H. murina). This is the
dwarf tapeworm of man and rodents. On account of its small
Size its presence in man is usually overlooked, except as found
in microscopic examination of feces.
Description. H. nana measures 5 - 50 mm. (2 inches or
less) in Tength and 0.5 = 1 mm. in width and is composed of 100
~ 200 proglottides; scolex minute, with four suckers and a
single row of minute hooks. There are three testes to each
segment. Mature and ripe proglottides are much broader than
long. The eggs are quite characteristic, elliptical, with two
membranes, the outer 30 - 60“ in diameter, the inner 16 - 30
and having at each pole a distinct knob, provided with thread-
like filaments.
life history. ~ The dwarf tapeworm is unique among the
cestodes of man in that the entire life cycle may be complete
in the single host. The embryonated eggs taken in with food or
drink, or from soiled fingers, liberate the hexacanth embryo
which bores into the intestinal mucosa. Here it transforms into
a minute cysticercoid, resembling the cysticercus of Taenia
saginata In general structure but differing from it in being of
Small size and lacking the fluid filled cavity. In less than a
160869
week this cysticercoid becomes mature and drops into the lumen
of its host, evaginates its head and attaches, and promptly
develops into a mature tapeworm in the same host that it
entered as an embryo. The entire cycle is completed in 15 -
20 days. is ;
Geographic distribution and prevalence. = The dwarf tape-
worm 18 a cosmopolitan species, though until the development of
the practice of making microscopic examinations of feces in
diagnosis work, it was rarely recognized. It is now considered
the most common tapeworm of man in the United States. Stiles
found it in 5 per cent. of the children of an orphanage in the
District of Columbia; Frey found it in 22.per cent. of the
children in a Texas orphanage. The worms occur in large num-
bers, more than 2000 having been recovered from a single host,
‘There is abundant evidence that it is injurious to its host,
Prophylaxis. - Since it.is clearly established that in-
fection of man by Hymenolepis nana may be acquired from rats
and mice, and that development is direct, without intermediate
host, it is obvious that protection of food from contamination
by these animals is essential, The danger of direct infection
from the human host must also be borne in mind. It is not un-
common to find the parasite infecting several or all members
of a family.
References. = Joyeux, 1916, 1920; Ransom, 1904; Stiles,
1903; Woodland, 1924. | se
HYMENOLEPIS DIMINUTA. ~ This species, which is likewise
common in rats and mice, has been noted as an incidental parasite
of man. Unlike H. nana, it requires an intermediate host in its
life cycle. coe
: Description. - H. diminuta is much longer than is H. nana,
since it varies in léngth from 20 = 60 cm. {8 - 24 inchés), and
in width from 3 - 4 mm. The rostellum is small, piriform, and —
is unarmed. Mature segments are 0.75 mm. long by 2.5 mm. broad,
Life history. ~- The larval stage is capable of developing in
a wide series Of insect hosts, chiefly cereal-infesting species.
The cysticercoids have been noted in the larva and adult of the
moth Pyralis farinalis, an earwig, Anisolabis annulipes, the ten-
ebrionid beetles, Akis spinosa, Scaurus striatus, and Tenebrio
molitor, the rat fleas Ceratephyllus fasciatus and Xenopsylla :
@heopis. There is even évidence that certain myriapods may serve
as intermediate hosts. The most frequent are the rat fleas and
‘the adults of the beetle Tenebrio molitor. When the infected in-
sects are fed to rodents the complete development of the tapeworm .
takes place in a little less than three weeks. |
4.608ye
70
Geographic distribution. - Something over 70 cases of in-
fection of man by this parasite are known and these are very
widely distributed geographically. Of the 17 cases occurring
in the United States, 3 are known to the writer to have been
found in Minnesota. Considering the fact that the infective
Stage occurs in an insect, it is natural that most of the re-
ported cases were in young children. It has been found in from
15 to 20 per cent. of the rats examined by the writer in Minneso-
ta and Brumpt found it in 55 per cent. of those examined in
Paris.
References. - Joyeaux, 1920; Ransom, 1904; Riley and Shannon,
1922.
RELATED SPECIES. +» Hymenolepis carioca is a very delicate,
thread-like species which sometimes Occurs in great numbers in
the intestine of chickens. Related species in water fowls are
known to undergo their early development in Cyclops and other
minute crustaceans. A systematic review of the avian species of
Hymenolepis and related genera is given by Mayhew, 1925.
Genus DIPYLIDIUM
Scolex with four round suckers and retractile rostellum
which is armed with three or more rows of minute hooks with broad
insertions. The reproductive organs are in duplicate, with a
pore on each side of the proglottis. The uterus of the ripe
segment breaks up into capsules which contain a number of epegs..
DIPYLIDIUM CANINUM, (Taenia cucumerina, T. elliptica). -
This is the commonest tapeworn of pet dogs and cats. Numerous
cases of its occurrence as an incidental parasite of humans, par-
ticularly young children, are on record.
Form and structure. - The mature worm is rather small and:
Slender, measuring from 10 ~- 40 cm. (1 - 4 in.) in léngth; the
retractile rostellum is provided with three or four rows of ,
minute, easily detached hocks; the sucksrs are relatively large
and ellipsoid. The mature proglottides somewhat resemble
cucumber seeds in shape and like others of the genus, are pro-.
vided with a genital pore on each side and with double sets of
reproductive organs. The mature segments may measure up to 1 cm,
in breadth.
Life history. - The eggs are discharged in brick-red
packets of 8 to I5, formed by diverticula of the uterus. As in
Hymenolepis, the larva is a minute cysticercoid. Melnikov, as
Tong ago a8 1869, showed that the intermediate host was the dog
louse and later it was found that the parasite also developed
in the dog or cat flea the embryos being taken up by the larva
1608ee
71
of the insect. The animal becomes infected by biting or licking
up its insect pests and the worm matures in about two weeks,
Human infections are due to the accidental ingestion of the
insect host, through feeding with, or fondling, cats and dogs.
Human infection. - Of the 76 cases summarized by Blanchard,
1914, S50 per cent. were of children less than six months old.
Vacca, 1909, noted infection in an infant of about twenty days.
On attempting to locate the source of this remarkably early in-
fection it was learned that a cat which had been brought into
the house six days after the birth of the child harbored 3l
specimens of Dipylidium caninum and on examination of fleas
from its fur cysticercoids were found.
References. - Blanchard, 1907, 1914; Diamare, 1893; Grassi
and Ravelli, I888; Melnikov = Razvedenkov, 1869; Riley, 1910.
RELATED SPECIES. ~ Dipylidium sexcoronatum, also occurring in
both dogs and cats, closély resembles D. caninum but may be dis-
tinguished by the fact that it has six rows of hooks on the
rostellum, instead of three or four. At least four other species
have been reported for the cat.
Genus DIPHYLLOBOTHRIUM
Tapeworms of the genus DIPHYLLOBOTHRIUM differ from those
already discussed in two important characteristics. The attach-
ment organs, on the scolex, are elongated, slit-like suckers
and the genital pore is in the mid-ventral line. The uterus :
forms a rosette, discharging its eggs through a pore, rather than
breaking down and scattering the eggs en masse. The forms in-
festing man have undergone unfortunate shifts in nomenclature,
being commonly classed as Bothriocephalus or as Dibothriocephalus.
DIPHYLLOBOTHRIUM LATUM. (Bothriocephalus latus.
Dibothriocephalus latus). = The broad tapeworm, or, fish tapeworm
or man is found as adult im the small intestine of man, dog, cat
and fox. The immature stage occurs as a worm-like plerocercoid
in the viscera and muscles of a considerable variety of Tish.
Structure. - The mature worm is the largest of the tape-
worms reported for man, since it may attain a length of 15 meters,
or éven more, and vossesses from 3000 to 4000 proglottides, The
Ovoid head has two long sucking grooves, or bothridia, The
proglottides are much broader than long and in their center is the
uterus in a rosette-like coil. The genital pore is situated on
the mid-ventral line and slightly further back is a second opening
through which the eggs are laid. The latter are large, elliptical,
brown, and are provided with a cap or operculum. They average in
size 70“ by 45.4 ,
1608oe
Development. - As in the case of the flukes, the dis-
chargéd éggs, after a considerable period in water, release a
ciliated embryo, which in this instance is known as a
coracidium. It swims about actively for a time and on being
taken up by certain minute crustaceans of the genus Cyclops
and related: forms, it loses its cilia and undergoes the first
stage of larval development. If the crustaceans are eaten by a
perch, pike or various other fish which serve as hosts, the
‘larval’ tapeworm works through the walls of the alimentary canal
and in the viscera or muscles it becomes the elongated worm-
like plerocercoid. Development is completed when this plerocer-
‘coid is taken in viable condition into the alimentary tract of
man ‘or of one of the carnivores which serve as primary hosts
of the tapeworm. Braun's experiments indicated that this re-
quires some five or six weeks, but, according to Parona, eggs
are discharged in 24 days after infection. The mature worm is
noted for its longevity, one case recorded by the writer having
served as host for over thirteen years.
Action on the host. = In addition to the usual gastro-intes-~
tinal disturbances, patients who harbor the broad tapeworm fre-
quently suffer from.a severe anemia, resembling pernicious anemia.
50 commonly is this associated with infection by this species |
that physicians recognize a “bothriocephalus anemia". It not
infrequently results in death if the worm is not expelled, but
promptly clears up if the parasite is removed. That this condi-
tion is caused by a toxine. secreted by the worm has been claimed
by various workers and seems demonstrated by the work of
Schaumann and Talquist, 1898. These investigators fed dogs on
fragments of the worm and in other.instances injected extracts
of the strobila. The result was marked anemia, the red blood
corpuscles being reduced from a normal of 7,200,000 to 3,400,000
per cubic millimeter.. |
Geographic distribution. - The broad tapeworm is widely dis-
tributed in Europe and in parts of Asia. It is also found in
Africa and in.the United States. In Europe it is especially
prevalent in the Baltic region and in Scandinavian countries. |
Until recently it was supposed that all cases noted in the United.
States wore imported, but it is now known that the’ infection is.
endemic in at. l@ast.tie Great.Lakes region, and Manitoba. 7
_ Prophylaxis. - According to Braun, it is necessary to cook
fish for at least ten minutes in order to insure the death of
the plerocercoids. An important factor in control measures is
the prevention of discharge of segments and eggs from patients
into water, and the resultant infection of crustaceans and fish.
It is significant that the first case of human infection by this
tapeworm which was known to have been contracted in the United
States: was in a town settled largely by families from endemic
16087O -
centers in Europe and that the sewage of the village was dis~ Ze
charged into a small lake in its limits. Magath found all the
pike and pickerel examined from this lake infested with the
plerocercoids of this tapeworm.
References. - Braun, 1881, 1883; Essex, 1927; Janicke and’ _
Rosen, 1917, (development); Magath; 1927, 1928; Riley, 1924, ww.
1928, (endemic centers in the U, S.); Schaumann and Talquist,
1898; Sommer and Landois, 1872, (anatomy); Vergeer, 1928.
RELATED SPECIES. - A few isolated cases of infections of
man-by other species of DIPHYLLOBOTHRIUM have been noted. Tape-
worms of this group occur in dogs and in various fish-eating
mammals and it is not improbable that they may be found as rare
. incidental parasites of man.
In this connection it should be noted that under the group
name SPARAGANUM there have been reported several instances of
the infection of subcutaneous and other tissues of man bw ~“*
larval forms related to Diphyllobothrium. These casee-are apy
parently very rare.
RELATED GENUS - Worms of the genus DIPLOGONOPORUS resemble
those of Diphyllobothrium in having suckers as slit-like |
furrows, and very short and broad proglottides, but the repro-
ductive organs are in duplicate in each proglottis, and there
‘ are two genital pores, submecian in position. The worms are
chiefly parasites of whales and seals but several noteworthy
cases of human infestation are known. It is probable that the
intermediate hosts are fish.
Genus ECHINOCOCCUS
Tapeworms of the genus Echinococcus are characterized by
the very small size of the strobila and by the fact that it is
composed of the head and three proglottides, of which only the
terminal is gravid. The larval stage is a thick-walled cyst
with many brood capsules containing scolices. The generic name
‘Taenia is usually applied to these worms but the characters
@iven are sufficient to necessitate classing in a separate
genus. One species is of very great significance in human and
veterinary medicine.
ECHINOCOCCUS GRANULOSUS. (Taenia echinococcus; Echinoc..
coccifer echinococcus). - This is the hydatid tapeworm which is
known chiefly by its very large, multiple-headed cysts, re-
ported for some 40 mammalian hosts, including man. The adult
is found in the dog, jackal and wolf, which are often heavily
.infected. Rarely, it has been noted in cats and can be trans-
ferred to them experimentally, though with difficulty.
160874
Apparently the most common of the intermediate hosts is the hog.
form and structure. - The echinococcus tapeworm is the
smallest of the several tapcworms affecting the dog, since it
measures only 3-6 mm (1/4 in) in length. It is composed of
three segments and the scolex. The head is very small, with a
prominent rostellum armea with a doubles row of hooks. The
terminal ripe proglottid comprises about one ralf of the entire
length of the worm. It contains from 400 to 800 eggs, a rée-
latively small number.
. Development. - When the eggs discharged with the feces of
tis’ dog: are taken up by one of the 40 or more mammals which may
serve as intermediate host, the embryos escape and pass to varie.
ous organs. A favorite location for cyst development is the
. liver, 46.4 per cent. of the recorded cases for man affecting
this-organ. Wext in preference are the lungs, with 8.76 per.
‘cent. of cases, but almost any tissue is liable to infection.
‘Having settled ina given tissue, development is very
slow. By the end of the fifth month the cyst is-about a centi-~
meter in diameter, but it is still several months or even years.
before head development occurs. It often attains the size of an
‘orange, and even that of an adult human head. Instead of one -
invaginated scolex 2 single cyst may develop thousands, each
capable of developing into a tapeworm when taken up by a dog.
These larval heads develop within brood capsules budded from. th:
inner wall of.-the cyst, and each contains from 1 to 120 heads.
Since: the entire cyst has developed from a single egg we have
here a. typé. of polyembryony. When ingested by the primary host
they complete their development in from.4 to 10 weeks. It is.
not surprising. that they” may occur in very large numbers, 3000
or more, in a.dog, since a single feeding on infected. organs _-_
would result in taking in great numbers of scolices, each capable.
of. developing into an adult in the primary host. .
Effects. - The hydatid tapeworm is the most dangerous of
‘those infecting man, although occurring only in the larval stage.
About-14 per cent. of the known cases resulted fatally. Frequent-
ly-the cysts do not produce any symptoms until secondary infec- —
tion,occurs, and.then there is the picture of an acute infection.
Adominal hydatids sometimes rupture spontaneously. and cause
death from the absorption of very toxic substances found in the
finid which fills the cyst. In other cases the rupture of the
cyst results in urticaria, due to sensitization of the host
against. hydatid antigen.
Geographic distribution and incidence. - The hydatid tape-
worm-:is very widely distributed. Notable centers of infection
have long. been Iceland, parts of. Australia, the Argentine
Republic and Uruguay. Some 350 cases of human infection have
; | “608yi
75
been reported for the United States, most of them imported
cases. It is significant that in recent years the cysts have.
been found in alarming numbers in cattle and hogs in Virginia,
Oklahoma, Arkansas, and Louisiana, thus indicating that dogs in
these regions carry the adult worms and are a menace to man.
Prophylaxis. - A consideration of the life history of the
hydatid tapeworm shows that the only feasible method of preven-
tion of the disease in man and animals is through control of
the primary host in regions where the parasite is endemic.
Organs infected with the cysts should be burned to prevent
their transfer to dogs; rigid precautions against contamination
of food and drink should be enforced, stray dogs should be
killed, and others treated and controlled.
References. - Blanchard, 1905, prophylaxis; Leuckart, 1886,
for detailed life history studies; Magath, 1921, for methods of
diagnosis; Johannides and Riley, 1924, for recent summary;
Teichmann, 1898, analysis of 2,452 case records.
Genus MULTICEPS
Under the genus Multiceps are classed several species of
tapeworms which resemblé Echinococcus in that the immature
stage develops many heads, or, in other words, is polyembryonic.
This cyst is known as a coenurus and differs from a hydatid
cyst in having a thin wall and in lacking brood capsules. The
adult worms are relatively large and are not to be distinguished
from those of the genus Taenia.: Like Echinococcus their primary
hosts are the dog and related carnivores.
MULTICEPS MULTICEPS. (Taenia coenurus; Coenurus cerebralis).
- One of the most important tapeworms of domesticated animals
is this species which is the cause of “gid" in sheep. It is
widely prevalent in Europe and there are apparently several
endemic centers in this country, the most serious being in
Montana. The eggs discharged from an infected dog or wolf are
taken up by sheep in grazing and the hexacanth embryo passes to.
the brain where it develops as a multiple~headed coenurus, which
may attain the size of a hen's egs. Death commonly results 7 to
9 months after infection. Wolves and dogs feeding on the dead.
animal continue the cycle. One well authenticated case of hu-
man infection by this cyst is reported by Brumpt.
References. - Brumpt, 1927, human case; Hall, 1910, general.
Seta oer
Ransom, 1905, presence in American sheep, and control.
RELATED SPECIES. - Multiceps serialis, another dog tapeworm,
is a common parasite-of- rabbits in this country, occurring. as
large,. many headed cysts:in the muscles. It seems most commonly...
found in jack-rabbits. This and related species are discussed by
1608ee
76
Hall, 1910 and 1919. The latter paper treats of the adult
taenoid cestodes of the dog, cat and related carnivores of
domesticated animals and even of man. Bearing on this topic
is also a valuable review by Hall, 1915. 3
Phylum NEMATHELMINTHES
References
In addition to the general texts see Baylis and Daubney,
1926; Hall, 1912; Hetherington, 1923; Neveu ~ Lemaire, 1912;
Ransom, 1911; Stiles and Hassall, 1920, 1926; Ward, 1923; Yorke
and Maplestone, 1926. :
The NEMATHELMINTHES, or threadworms, are characterized by
their cylindrical, spindle-shaped, or thread-like, unsegmented
body covered by a thick cuticle. The so-called body cavity is
usually spacious. The sexes are, with few exceptions, separate. |
The phylum is a large one and contains both parasitic and free~-
Living forms.
The classification of the group has long been in an un-
satisfactory condition which Yorke and Maplestone's comprehen~
sive treatment of those infecting vertebrates will do much to
clarify. Since their treatise will be the standard guide for
years to come, we shall use their major groupings, even though
they differ somewhat from those at present most used in
literature.
Yorke and Maplestone recognize two classes, the NEMATODA
and the ACANTHOCEPHALA, or thorny-headed worms. ‘The members of
the Nematoda possess an alimentary canal but lack a proboscis,
those of the Acanthocephala lack an alimentary canal but possess
a proboscis which is usually protrusible and almost invariably:
furnished with hooks. ,
The class NEMATODA contains two orders, the Eunematoda and
the Gordiacea. : 3
The EUNEMATODA are "nematodes in which the body cavity is
not lined by epithelium, the gonads being continuous with their
ducts. Occasionally the posterior portion of the alimentary
canal may atrophy in the sexually mature worms. Lateral chords
present; cloaca absent in the female." .
The GORDIACEA are the sdé-called "hair-snakes"and are often
placed in a separate class, the Nematomorpha. The most obvious
characteristic is the absence of an alimentary canal in the
adult stage. "The body cavity is lined by epithelium; the gonads
are not continuous with their ducts, the ova being discharged
1608AE onssage cerns
77
into the body cavity and then passing into the ducts". “Lateral
chords absent; cloaca present in the female".
The species of chief economic importance in the higher
animals belong to the order EUNEMATODA, defined by Ward, 1916.
In addition, this order contains many species parasitizing in-
vertebrates, some very important enemies of plants, and a vast
number of free-living forms. Many of the species infesting
animals pass a part of their life cycle free in the water or in
damp earth.
The majority of the nematode parasites of the higher
animals are oviparous, though some are viviparous, notably
Trichinella spiralis and Filaria bancrofti. The eggs may be pro--
vided with a firm resistant shell, serving to protect the embryo
or unhatched larvae from unfavorable conditions. Such, for
instance, is the case with the eggs of various ascarid parasites
and of the whipworms of man and animals, which may live for
months or even years in viable condition in the soil. Others, ©
such as hookworm eggs, are thin-shelled and hatch soon after
their discharge.
The newly hatched larvae typically undergo two molts before
they become infective. In some cases the second larval skin
remains as a sheath to be cast off as the infective third stage
enters its definitive host. After entrance into the host there
are two additional molts before sexual maturity is attained.
Development may be either direct (Ascaris, and whipworm)
or through an intermediate host (Trichinella, Filaria).
Entrance to the host may be either active or passive, but
the studies of recent years have shown that even in the latter
case there are often complicated migrations in the host body
before maturity is attained.
_ Eight superfamilies of the Eunematoda are recognized by
Yorke and Maplestone, who give the following key for their
separation:
1. Heterogenetic, parasitic form par-
msenomenetic . « «6 « -» Rhabdiasoidea.
Not heterogenetic, parasitic forms
sexually differentiated. . 2
1608hs
iid 7 ;
78
Oesophagus consisting of a narrow
tube running through the centre
of a row of single cells for most
OF 208 260nth . 9s
Oesophagus not consisting of a
narrow tube running through
the centre of a row of single cells
Males with a bursa copulatrix. ,
Males without a bursa copulatrix .
Bursa copulatrix cuticular and
supported by rays . . .
Bursa copulatrix muscular and
not supported by rays . . .
Oesophagus dilated posteriorly
into a bulb usually containing
a denticular apparatus and fre-
quently separated from the rest
of the oesophagus by a con-
BEPSGCLON 6 6 ok 8
Oesophagus not dilated posteriorly
5-9 OB OULU. 6 A OS
Head with three large lobes or
lips: relatively stout worms. .
Head without three large lobes or
lips but with two lateral lips, or
4 or 5 small lips, or lips absent;
relatively slender, filiform worms;
Usually with two lateral lips,
chitinous buccal cavity or
vestibule usually present, vulva
usually in the middle of the body
or posterior to it; parasites of
alimentary canal, respiratory
system, or orbital, nasal, or oral
GCOVAGLGS «2 0 4
Usually without lips, buccal cavity
or vestibule absent or rudi-
mentary, vulva almost invari-
ably in the oesophageal region;
parasites of circulatory or lym-
Phatic systems, or muscular, or
connective, tissue, or of serous
CAViGiCS 1. 2 «© +2
1608
Trichuroidea.
Strongyloidea.
Dioctophymoidea.
Oxyuroidea.
Asecaroidea,.
Spiruroidea,
Filarioidea.79 !
‘Without attempting to enter into details of classifica-
tion, we shall quote the summarized characteristics of these
superfamilies and consider under each a very limited number of
important species.
Superfamily ASCAROCIDEA
"Bunematoda; usually fairly large and stout; head bilobed;
oesophagus frequently more or less enlarged posteriorly, but
without a definite spherical posterior bulb containing 4
valvular apparatus (except in Dujardinia, where there is a
small, unarmed bulb), with or without diverticula. Spicules
equal or unequal. Females not much larger than the males.
ASCARTS LUMBRICOIDES. - This is a cosmopolitan and one of
the most common of the intestinal parasites of man. The same,
or at least a very closely related species is a very common
parasite of pigs.
Description. - The mature males measure 15 - 17 cm., the
females 20 - 25 om., and are pointed at both ends. They are of
a pale yellow or whitish color, somewhat resembling a large
earthworm. The head is provided with three lips - a dorsal
and two latero-ventral, - bearing papillae. The caudal end of
the male is-curved towards the ventral side and bears two
spicules. In the female the caudal end is conical and straight.
The vulva is situated about the anterior third of the body.
The eggs, of which a single female may produce more than
26,000,000 are ellipsoidal, 60 - 75” x 40 ~ 50” and are
covered by a transparent, mammillated albuminous sheath which
gives them a very charscteristic appearance. They are dis-
charged in an unsegmented condition.
Development. - The eggs in the presence of moisture and
warmth undergo repeated segmentation and in 30 ~ 40 days
develop infective larvae. In regions with sustained high tem-~
perature and moisture this period may be considerably reduced.
They are capable of resisting dessication and other unfavorable
conditions for long periods. Davaine kept them for 5 years in
water and it is probable that they live even longer in moist
earth. When taken in food or drink by the human host, the
‘larvae are released in the stomach. It was formerly supposed
that they immediately made their way to the intestine and there
developed directly into the mature worm. The researches of
Stewart, Ransom, and others have shown that the liberated larvae
pass to'the liver and then to the lungs, appearing in the latter
organs about a week after ingestion. By the tenth day they are
migrating up the trachea, whence they enter the oesophagus and
then pass down into the intestine. Here they complete their
development and are discharging eggs in about a month's time
after being taken into the body. In the course of their
160880
migration through the body cf the host, larvae may be carried
to developing young in the uterus and thus prenatal infec-
tions arise, although the experiments of Martin, 1926, would
indicate that this does not occur as readily as has been
supposed.
Effects on the host. - Ascaris lumbricoides may be present
in ereat numbers in the human host. in extreme cases upwards
of 1000 have been reported and instances of 100 or more are not
uncommon.
strongyloid larvae which resem le
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SUP ft ppl ess
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en by
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Referencése = Sanagrounc 1926, includes extensive
LVN i Sis < 3
71 > | “~* a |
bibliography -«
qo J
PTs LOT capiwy?r ee wate Va HO ~ i | ‘ 5 « 45 ¢
RELATED SPROUL. = Cisse ly relatec species occur in bie GOK,
ae eg ae an c 2 c 2 i 9 . x mal
rabbit and sheep and various other mammeis.
(_ Rhebdconema nigrovenosum, angiosvomum
ae TAC I ; — AVA CY $ tha . met aa We gee a
nicrovenosum) S Nei y ,OMmmon 172 the lunges nr Ere -3,600aTC. 12C0r
Ce se
>. ea 3 Amn aATtAe Nhe mone Levey “ar fees LWe
Sana oipiens, and otnerse the e ges + Une
we i j > coc
j menregregeny er oy P > and ar aw ft
trachea of the frog and are then sw of
1608ty
o7
development to the hatched larvae are to be found in the in-
testines When they reach the exterior, if the temperature is
high, they soon transform into adult males and females. The
fertilized female produces rhabditiform larvae which enter the
larynx of frogs and thence pass to the lungs.
GORDIACEA
The GORDIACEA are long slender, hair-like worms popularly
known as “hair-snakes". ‘The body is cylindrical, with a blunt
or rounded head end and is ornamented with various areoles,
scales and papillae. The alimentary canal is present in larval
forms but is atrophied in the adult worms.
The early stages are parasitic, chiefly in the larvae of
aquatic; insects, though they have been reported for spiders,
oligochaete .worms trematodes (Cort, 1919) and even for fish
and frogs. | The older larvae are very commonly found in grass-
hoppers, crickets. and some other terrestrial insects. They
play an important role in the natural control of some of these
{here are various records of the occurrence of species of
Gordiacea as incidental parasites of man but as Brumpt points
out, these are very questionable and can be established only by
carefully conducted experiments.
‘References. - May, 1919; Montgomery, 1904; Ward and Whipple,
1918.7
Class ACANTHOCEPHALA
The Acanthocephala are characterized typically by the
presence Of a protractile proboscis, armed with numerous ‘hooks.
The alimentary canal is lacking. The larval stagés are found
in certain crustacean, insects, fish-and small mammals. The-
adults, are. especially abundant in birds and: fish. In.recent.
years Van Cleave has undertaken a comprehensive study of our
North American forms and has added greatly to the knowledge ‘of
the group, |
Two and possibly three species are recorded as rire m
parasites of man..
ECHINORYNCHUS GIGAS (Gigantorhynchus gigas)-.-Thig.is“a..
common parasite of hogs which attains about the same .Sike as,
Ascaris lumbricoides but which is immediately distinguishable «|
its Spiny proboscis, buried deep in the intestinal wall, and poy
its slight, superficial annulations. The eggs are 90 ~- 100". ~
long, nearly cylindrical with a three-layered: sholl. .of which the
L608“age
98
middle is the thickest. The discharged eggs, containing well
developed embryos, are taken up by the larvae or "opubs" of
May-beetles, which serve as intermediate hosts. Records of
human infections by the adults are very rare, put apparently
well established.
MONILIFORMIS MONILIFORMIS (Echinorhynchus montiformis) is
a normal parasite of rodents but is capable of developing in
man. Its intermediate host is a cockroach, Blaps mortisaga.
References. - Chandler, 1921, Moniliformis in U, eet.
Grassi and Calandruccio, 1888, life history of Moniliformis ;
Kaiser, 1893, general treatise; Luhe, 1911, systematic; Van
Cleave, 1919, et al., North American forms.
HIRUDINEA
_ The HIRUDINEA, or leeches, belong to the phylum Annulata,
having the body composed of similar segments, a body cavity,
and an alimentary canal furnished with two openings. From other
members of the phylum the leeches are distinguished by having
the body marked externally by secondary rings and by having at
each end a sucker. ‘The mouth, at the base of the anterior
sucker, possesses, typically, three cutting plates.
Leeches are temporary parasites or, may directly attack
smaller forms as predators. As parasites they attach to the
skin, or to mucous linings of the nose, mouth and similarly
accessible cavities. While most of the species are aquatic, ©
the land leeches of India, the Philippines, Australia and South
America are famous for their attacks on man and animals.
‘Their action on man depends on their numbers and localiza-.
tion. The mouth parts are so developed as to cause free bleeding
which may continue after the leech is gorged and leaves its host.
Since their attacks are practically painless a considerable loss
of blood may result before they attract attention. When they are
accidentally taken in with drinking water and attach in the
pharynx, or nose, or similar locations they may do serious damage.
Horses are particularly liable to this form of attack, the
‘parasites attaching to the lips, cheeks, pharynx or other parts
of the mouth. In severe cases it is necessary to remove them
with forceps or by the hand wrapped in a towel.
Some species have a poisonous saliva, causing inflammation,
urticaria and more or less serious nervous trouble. Others are
.-’ ‘known to be carriers of trypanosomes of cold-blooded animals and
4t is believed that “mal-de-caderas", a South American
trypanosomiasis of horses is similarly carried.
160899
Formerly, leeches were much used medically to produce
bleeding, and they were not oly collected for sale but were
cultivated in great numbers. Professor Nachtrieb states that
one American leech farm sold as many as 1000 or more & day.
"Today leeches are so seldom used that few young people have
seen a medical leech, and most physicians of today do not know
how to apply a leech properly".
--. References. ~ Moore, 1918; Nachtrieb, Hemingway and
Moore, I9IZ,
BIBLIOGRAPHY
(See, also, the list of comprehensive texts, PP. 13S: 3)
The bibliography of animal parasitology is so extensive
that the most which can be done here is to call attention .to
a few papers which are comprehensive, or which are of local
interest. Text references not included may be located through
the Quarterly Cumulative Index to Current Medical Literature.
AcKkert, J. E. and Payne, Florence K., 1920. Investigations on
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Adie, H., 1915, The sporogony of Haemoproteus columbae. Indian
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Alexander, M. E., 1923. Trichiniasis, endemic and sporadic,
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Ashford, B. Ke and Gutierrez Igaravidez, P., 1911. Uncinariasis
(hookworm disease) in Porto Rico:= a medical and economic
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Augustine, D. L. 1925. Investigations on the control of hook-
worm Qisease. xxiii. Experiments on the factors determin-
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jour. Hyg. 3 (4): 420-443. Numerous other papers bearing
on this topic, in same journal 102e -
1608LOO
Augustine, D. L., and Smillie, W. G. 1926. The relation of
the type of Soils of Alabama to the distribution of hnook~
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and genera of Nematoda. xxxvi + 277 pp. British Mus.,
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Becker, E. R., 1923a Observations on the morphology and life
cycle of Crithidia gerridis.. Patten, in the water strider,
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Observations on the morphology and life history of
Herpetomonas muscae-domesticae in North American muscoid
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citelli sp. nov. from the striped ground squirrel Citellus
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Benham, W. B., 1901. Platyhelmia, mesozoa and nemertini. In E.
Ray Lankester, Treatise on Zoology, pt. 4. 212 pp. London.
Ben-Harel, S., 1923. Studies of bird malaria in relation to the
mechanism of relapse. Amer. Jour. Hyg. 3: 652-685.
Bensen, W., 1909. Untersuchungen uber Trichomonas intestinalis
und vaginas des Menschen. Arch. f. Protistenkunde, 18:
Lid ws D Se Fad.
Bettison, W. L., 1926. Trichinosis. Report of four cases,
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Blanchard, R., 1905. Prophylaxis de la maladie hydatique. Arch.
ce parasitol. 9: 451. 1907. Parasitisme du Dipylidium
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Arch. de parasitol. ll: 459-471. lgl4. Encore un cas de
Dipylidium caninum a Paris. Arch. de parasitol.
°
. - °
ees
Boeck, W. Ge, 1921. On the longevity of human intestinal
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1608ag
101
Boeck, W. C. and Drbohlav, J., 1925. The cultivation of
Hndamoeba histolytica. Amer. Jour. Hyg. 5(4): 371-407.
Boeck, W. C. and rete C. W., 1925. Studies on various in-
testinal parasit s (especially amoébae ) of man. Bull. No.
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Braun, M., 1881. Zur Frage des Zwischenwirthes von Bothriocepha-~
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