length, 2.5 to 4 millimeters in maximum breadth; composed of 800 to
1,300 segments. Head small, almost globular; 200 to 600μ in width;
rostellum rudimentary, pyriform, only slightly protractile; hooks
absent; suckers globular, near the apical portion of the head, 80 to
160μ in diameter. Neck usually short. Segments throughout strobila
broader than long. Genital pores on left margin, near the junction of
the anterior and middle thirds of each segment. Three testes in each
segment; vas deferens dilates into a prominent seminal vesicle before
entering the cirrus pouch, within which also is a vesicle. Gravid
uterus occupies most of the proglottids; its cavity is subdivided into
a large number of incompletely separated compartments filled with
eggs. Eggs round or slightly oval; outer membrane 54 to 86μ in
diameter, yellowish in color, may be radially striated; inner membrane
24 by 20μ to 40 by 35μ in diameter, with mammillate projection at each
pole often not apparent; between outer and inner membranes a prominent
third layer of albuminous substance, often appearing as two delicate
smooth membranes, with intervening space filled by a granular
coagulum; embryonal hooks 11 to 16μ in length.
[Illustration:
FIG. 27.—Male and female organs of _H. diminuta_: _c. p._, cirrus
pouch; _g. p._, genital pore; _ov._, ovary; _rec. sem._,
receptaculum seminis; _s. g._, shell gland; _t._, testiculæ; _ut._,
uterus; _vag._, vagina; _v. def._, vas deferens; _v. ef._, vas
efferens; _ves. sem._, vesicula seminalis; _y. g._, yolk gland.
Enlarged. (After Zschokke, 1889, pl. 2, fig. 22.)
]
[Illustration:
FIG. 28.—Gravid segment of _H. diminuta_. Enlarged. (After Grassi,
1881, pl. 11, fig. 15.)
]
[Illustration:
FIG. 29.—Egg of _H. diminuta_ from man. Greatly enlarged. (After
Bizzozero, 1889a, pl. 4, fig. g″.)
]
HABITAT.—Adults in small intestine of brown or Norway rat (_Mus
decumanus_), black rat (_M. rattus_), house mouse (_M. musculus_),
Egyptian or roof rat (_M. rattus alexandrinus_), wood or field mouse
(_M. sylvaticus_), _Rhipidomys pyrrhorhinus_ [according to Linstow,
1878a, 23], and man (_Homo sapiens_).
DEVELOPMENT.—The larval stage (_Cercocystis H. diminutæ_) occurs in
larval and adult meal moths (_Asopia farinalis_); in young and adult
earwigs (_Anisolabis annulipes_); and in adult beetles (_Acis spinosa_
and _Scaurus striatus_).
GEOGRAPHIC DISTRIBUTION.—Massachusetts, Pennsylvania, Nebraska, Iowa,
District of Columbia, Maryland, Brazil, Italy, Germany, France,
Austria.
This parasite is certainly more common in man in this country than has
heretofore been assumed, but fortunately it seems to be one of the most
harmless and most easily expelled tapeworms occurring in man.
[Illustration:
FIG. 30.—Encysted cystic stage of _H. diminuta_: _caud._, caudal
appendage; _cyst._, adventitious capsule inclosing the cercocystis.
Enlarged. (After Grassi & Rovelli, 1892a, pl. 4, fig. 1.)
]
From present evidence, the rats and mice are looked upon as the regular
hosts for this worm, and hence as the natural reservoir of the
infection. The intermediate host becomes infected from the rodents and
then transmits the infection to man.
It might be mentioned that as yet no extensive study has been conducted
in the United States to differentiate clearly the various species of
_Hymenolepis_ found in our rats and mice. The possibility is therefore
not entirely excluded that some of our cases of _Hymenolepis diminuta_
may eventually be shown to be referable to other species of the same
genus.
NEMATODA—TRUE ROUND WORMS.
Family TRICHINELLIDÆ.[AA]
Footnote AA:
SYNONYM.—_Trichotrachelidæ._ It becomes necessary under the
international code to change the family name; the family name
_Trichinellidæ_ is chosen as less likely to lead to confusion than a
family name based upon _Trichuris_.
FAMILY DIAGNOSIS.—_Nematoda_: Elongate cylindrical worms; cephalic
portion long and very slender, caudal portion more or less swollen.
Mouth rounded, without lips. Esophagus relatively very long, composed
of a single row of large cells, forming the so-called “cell body” and
supporting a narrow esophageal tube; anus terminal or nearly so.
Male: With a single spicule or without spicule.
Female: With one ovary; vulva near caudal end of cell body, close to
point where body increases in diameter; oviparous or viviparous.
Eggs: Oviparous species, with thick shell, with opening at each pole,
closed by a transparent plug.
TYPE GENUS.—_Trichinella_ Railliet, 1895.
This family furnishes two parasites to man: The whipworm (_Trichuris
trichiura_) of the colon, and the trichina or flesh worm (_Trichinella
spiralis_, see p. 101).
Genus TRICHINELLA[AB] Railliet, 1895.
Footnote AB:
SYNONYMS.—_Trichina_ Owen, 1835 [not Meig., 1830, insect.];
_Trichinus_ Fraser, 1881a, for _Trichina_.
GENERIC DIAGNOSIS.—_Trichinellidæ_: Very minute worms, of nearly
uniform diameter. Adults in intestine of mammals, larvæ encysted in
muscles.
Male: Without spicules, but with 2 conical appendages on the tail, at
side of terminal cloacal opening.
Female: Vulva about one-fifth the length from anterior end;
viviparous.
TYPE SPECIES.—_Trichinella spiralis_ (Owen, 1835) Railliet, 1895.
TRICHINELLA SPIRALIS (Owen, 1835) Railliet, 1895.
[Figs. 31 to 51.]
SPECIFIC DIAGNOSIS.—_Trichinella_: Body thread-like, visible to naked
eye.
Male: Length, 1.4 to 1.6 millimeters; diameter, 40μ; distal of cloacal
opening, 2 pairs of papillæ, the anterior pair hemispherical,
posterior pair conical.
Female: Length, 3 to 4 millimeters; diameter, 60μ; anus terminal;
vulva one-fifth of length of body from the mouth; viviparous.
HABITAT.—Adults in lumen and wall of small intestine, encysted larvæ
in muscles of various mammals, particularly in rats, mice, swine, and
man.
GEOGRAPHIC DISTRIBUTION.—More or less cosmopolitan.
SOURCE OF INFECTION.—From the life cycle of this parasite it is clear
that the permanent reservoir of infection must be some animal with
cannibalistic tendencies. Of the three most important hosts (man, swine,
and rats), the rats present ideal conditions in this respect. It is true
that there are some tribes of man which are cannibalistic, but their
distribution is restricted. Likewise swine are in so far cannibalistic
that they eat uncooked swine offal and swill, but this is due to the
shortsightedness of man rather than to the habits of the swine.
Accordingly, neither man nor the hog presents the proper theoretical
conditions for the perpetuation of the parasites and hence to serve as
reservoir for the disease it causes.
Rats, on the contrary, are cannibalistic, and trichinosis is a common
disease among them. Hence they may be viewed as the natural reservoir
for the parasites and for the disease it causes; hence, also, any
well-directed public health campaign against trichinosis should consider
the eradication of rats.
Rats become infected by eating each other; by eating scraps of pork
found on the offal pile of slaughterhouses, or in swill; and by eating
scraps of human flesh in dissecting rooms of medical schools.
[Illustration:
FIG. 31.—Female trichina from the intestine; 24 hours after infection.
Enlarged. (After Leuckart, 1866a, pl. 1, fig. 1.)
]
Swine become infected by eating rats, and by eating scraps of pork on
the offal pile of slaughterhouses, or in swill.
Man becomes infected almost exclusively by eating pork and boar meat.
The rare infections which occur from eating other meat are almost
negligible.
MEDICAL SIGNIFICANCE.—_Trichiniasis_ or _trichinosis_ refers to
infection with the trichina or flesh worm. Normally it occurs only in
mammals, chiefly carnivorous and omnivorous species, and it is
transmissible from any infected mammal to any other mammal susceptible
to it, in case the latter eats the uncooked flesh of the former.
_Symptoms._—In heavy infections there may be three more or less distinct
periods of the disease, corresponding to the three stages in the life
cycle of the parasite; but these stages are obscure in light or in
repeated infections. Profuse sweating may last during the entire attack.
[Illustration:
FIG. 32.—Gravid adult female trichina. Enlarged. (After Leuckart,
1866a, pl. 1, fig. 2.)
FIG. 33.—Adult male trichina from the intestine. Enlarged. (After
Leuckart, 1866a, pl. 1, fig. 5.)
FIG. 34.—External genitalia of same. Enlarged. (After Leuckart, 1866a,
pl. 1, fig. 7.)
FIG. 35.—The same with extruded cloaca. Enlarged. (After Leuckart,
1866a, pl. 1, fig. 8.)
FIG. 36.—Cephalic portion of a trichina showing central nervous system
and anterior portion of intestinal canal. Greatly enlarged. (After
Leuckart, 1866a, pl. 1, fig. 13.)
FIG. 37.—Transverse section of a female trichina. Greatly enlarged.
(After Leuckart, 1866a, pl. 1, fig. 16.)
FIG. 38.—Young trichina embryo in a muscle fibre. Greatly enlarged.
(After Leuckart, 1866a, pl. 2, fig. 1.)
]
Period of ingression: The adult parasites are in the intestine, hence
gastro-intestinal symptoms develop; irregular appetite, nausea, diarrhea
or constipation, colicky pains; a temporary edema around eyes about the
eighth day; muscular pains begin.
Period of digression: This begins about the eighth to the fifteenth day,
sometimes later; young embryos are wandering to and attacking the
muscles, hence muscular symptoms (myositis) develop; painful tension of
muscles, especially biceps; members assume semiflexed position;
movements, chewing, swallowing, breathing, and speech become difficult;
eyes become fixed; fever.
[Illustration:
FIGS. 39–42.—Later stages of same; the muscular structure is
undergoing changes. (After Leuckart, 1866a, pl. 2, figs. 3, 6, 7,
8.)
FIGS. 43–45.—Muscle trichinæ, 0.3 mm., 0.4 mm., and 0.6 mm. long.
(After Leuckart, 1866a, pl. 2, figs. 10–12.)
]
Period of regression: The parasites become encysted in muscles. All
symptoms may increase, then gradually decrease; cachexia and anemia
resulting from malnutrition; pruritis, miliary cutaneous eruptions;
desquamation; about twenty-fourth day, a “second” edema develops,
especially about the face; lungs may become edematous; bronchial
catarrh, pneumonia, or pleurisy may appear; gradual recovery.
[Illustration:
FIG. 46.—A female trichina from the muscle. Greatly enlarged. (After
Leuckart, 1866a, pl. 1, fig. 12.)
]
[Illustration:
FIG. 47.—A piece of pork with encysted trichinæ. Enlarged. (After
Braun, 1903, p. 251, fig. 195.)
]
_Lethality._—The lethality varies from 0 to 100 per cent; it averaged
5.6 per cent in 14,820 cases collected from literature; it is dependent
upon amount of infection which remains in the body; low before second
and after seventh week, highest from fourth to sixth week.
_Prognosis._—Better in cases having severe diarrhea in first stage.
_Complications and sequelæ._—Abortion, menstrual disturbances,
pneumonia, pleurisy, peritonitis.
[Illustration:
FIG. 48.—Section through a rat’s muscle; the infected muscle fiber has
lost its striation, its nuclei are enlarged and increased in number.
Greatly enlarged. (After Hertwig-Graham, see Braun, 1903, p. 284,
fig. 212B.)
FIG. 49.—Portion of an isolated trichina cyst, at the pole of which
connective tissue cells have wandered into the thickened sarcolemma.
Greatly enlarged. (After Hertwig-Graham, see Braun, 1903, p. 284,
fig. 212C.)
]
_Clinical diagnosis._—Make microscopic examination:
(1) Of pork, if any has been left, to find encysted larvæ; if larvæ are
found, feed pork immediately to two or three guinea pigs or _white_
rats, to determine if the encysted larvæ are alive; kill one rat after
three days and examine intestinal content for adult; kill the second rat
after two weeks, the third rat after three weeks, and hunt for larvæ in
muscular portion of diaphragm. Even if live trichinæ are found in
intestine, an examination of the muscles may show that the worms were
too weak to reproduce, hence prognosis is favorable.
(2) Of patient’s blood, for increased proportion of eosinophiles.
(3) Of patient’s stools, for discharged adult worms, especially if
diarrhea is severe; dilute the fecal matter with warm water and pour off
whatever floats; place remainder in a shallow glass dish so that it will
not be over one-twelfth of an inch deep; move the dish gently around
over a dark background (such as dark paper), and hunt for small
hair-like objects; place these, if found, in a drop of water on a slide,
cover with a cover slip, and examine under low power. Or, if necessary,
make a microscopic examination.
(4) Of small excised portion of patient’s deltoid, about three to four
weeks after infection, for encysted larvæ; cut a small piece parallel to
muscle fibers, tease this on a slide, add a drop of pure water, or water
and glycerine, cover with another slide, flatten gently by pressure
while examining under low power.
[Illustration:
FIG. 50.—Calcified trichinæ in uncalcified cysts, from pork. Enlarged.
(After Ostertag, see Braun, 1903, p. 285, fig. 213.)
]
Suspect trichinosis especially under following circumstances: Several
patients in same family or in same neighborhood, usually of North German
descent, show typhoid-like symptoms shortly after a celebration
(wedding, birthday party, etc.) at which pork was served.
[Illustration:
FIG. 51.—Three phases of calcification of trichinæ and their cysts,
the changes starting from the poles of the cysts. Enlarged. (After
Ostertag, see Braun, 1903, p. 285, fig. 214.)
]
_Differential diagnosis._—Consider especially typhoid fever and
rheumatism.
_Treatment._—Purge in early stage to carry away the adult worms and thus
eventually decrease the amount of muscular infection. No treatment is
known which can be relied upon to kill the larvæ in the muscles; benzine
has been suggested. Stimulants may be given to carry patients through
until the larvæ encyst.
PROPHYLAXIS.—_Kill off rats and mice._—Educate public to eat pork only
when thoroughly cooked or thoroughly cured. A practical test of cooking
is the white color of the meat on being cut; if the cut surface is
reddish and serous, the pork is not sufficiently cooked to kill
trichinæ.
As a matter of practical experience, the microscopic inspection of pork
has not given the protection it is generally supposed to give. Of 6,329
cases with 318 deaths reported for Germany during the years 1881–1898,
3,388 cases with 132 deaths are directly attributable to faults in the
inspection. This system directly increases the tendency to eat raw pork,
gives the public a false sense of security, and does not give practical
results commensurate with its expense.
ACANTHOCEPHALA—THORN-HEADED WORMS.
Genus GIGANTORHYNCHUS Hamann, 1892.
GENERIC DIAGNOSIS.—_Acanthocephala, Gigantorhynchidæ_: Large worms
with annulate round to flat, tape-like body. Hooks with 2 roots and
completely covered with transparent chitin. Proboscis sheath a
muscular apparatus, without cavity. Central nervous system caudad of
equator of proboscis sheath and eccentric. Lemnisci long, cylindrical,
with central canal.
TYPE SPECIES.—_Gigantorhynchus echinodiscus_ (Diesing, 1851).
The Moniliform Thorn-headed Worm—GIGANTORHYNCHUS MONILIFORMIS
(Bremser, 1819).
[Figs. 52 to 58.]
SPECIFIC DIAGNOSIS.—_Gigantorhynchus_ (p. 108): Body attenuated
anteriorly, with fine transverse striæ or rings, or even constrictions
which give the appearance of a series of beads, except in the caudal
fourth of body, which is nearly smooth and cylindrical. Proboscis 425
to 450μ long, 176 to 190μ in diameter, armed with feeble, very curved,
26μ long, hooks arranged more or less in quincunx and forming at most
15 transverse and about 12 longitudinal rows. Lemnisci more than a
centimeter in length, cylindrical, undulated posteriorly.
Male: Length 4 to 4.5 centimeters long; bursa campaniform.
Female: Length 7 to 8 centimeters (to 27 centimeters after Westrumb).
Eggs: Ellipsoidal, 85 by 45μ; external envelope thin, yellowish;
middle envelope very thick, colorless, homogeneous; inner envelope
less thick, colorless, and quite pliant. Embryo striated transversely
in posterior two-thirds, and covered with spines which increase in
size toward anterior end of embryo, the anterior spines being
transformed into hooklets with prong and base.
Development: With beetles (_Blaps mucronata_) as intermediate host.
HABITAT.—Small intestine of various small mammals; brown rat (_Mus
decumanus_); white rat (_Mus norvegicus albus_); _M. fuscirostris_;
hamster (_Cricetus frumentarius_); dormice (_Myoxus quercinus_ or
_glis_); field mole (_Arvicola arvalis_ or _agrestris_?); _Lemnus
arvalis_; and _Mustela putorius_. It can also develop in man, as has
been shown experimentally by Grassi and Calandruccio (1888, 521–525).
MEDICAL SIGNIFICANCE.—Grassi and Calandruccio report a doubtful case of
infection in a girl near Catania. Calandruccio infected himself
experimentally by swallowing the young worms taken from a Blaps. Twenty
days later he was seized with severe pains which increased on pressure;
diarrhea followed, with ringing in the ears, fatigue, and somnolence.
Seventeen days later the characteristic eggs were found in his stools,
and twelve days later the symptoms became so severe that he took 8 grams
of extract of male fern; one to two hours later he passed 53 of the
parasites. For two days the symptoms continued, on the second day fever
developed, but all symptoms disappeared on the third day.
[Illustration:
FIG. 52.—_Gigantorhynchus moniliformis_, female. ×2. (After Grassi &
Calandruccio, 1888, p. 523, fig. 1.)
FIG. 53.—_G. moniliformis_, male. ×2. (After Grassi & Calandruccio,
1888, p. 523, fig. 2.)
FIG. 54.—Rostellum of _G. moniliformis_. Greatly enlarged. (After
Grassi & Calandruccio, 1888,
p. 523, fig. 3.)
FIG. 55.—Hooks from same. Greatly enlarged. (After Grassi &
Calandruccio, 1888, p. 523, fig. 4.)
FIG. 56.—Eggs of _G. moniliformis_, with embryo. Greatly enlarged.
(After Grassi & Calandruccio,
1888, p. 523, fig. 5.)
FIG. 57.—Egg very greatly enlarged. (After Grassi & Calandruccio,
1888, p. 524, fig. 6.)
FIG. 58.—A young larva of _G. moniliformis_ in a _Blaps_; the
rostellum is invaginated and the larva is
surrounded by a thick inner jelly-like and thin outer cuticular
covering. Enlarged. (After Grassi &
Calandruccio, 1888, p. 524, fig. 7.)
]
ARACHNOIDEA.
Genus LINGUATULA Frœhlich, 1789.—Tongue worms.
Species LINGUATULA SERRATA Frœhlich, 1789.
The larva of this parasite is found encysted in the entrails of rabbits,
cattle, and certain other animals, and it becomes mature in the nasal
cavities of canines.
Both the larva and the adult have been reported for man, and the larva
has been reported as occurring in _Mus decumanus_.
As canines are not fond of eating rats, the presence of the larval
tongue worm in the latter is of more academic interest than practical
importance, and although the theoretical possibility must be admitted
that a dog by eating rats might become infected with tongue worms and
eventually might transmit the infection to man, these possibilities seem
somewhat remote. Remote possibilities must also be admitted to the
effect that if a person ate a rat infected with tongue worms this person
might become infected.
COMPENDIUM OF ANIMAL PARASITES REPORTED FOR RATS AND MICE (GENUS MUS).
By CH. WARDELL STILES, Ph. D., _Public Health and Marine-Hospital
Service_,
and
ALBERT HASSALL, M. R. C. V. S., _Assistant, Division of Zoology, United
States Bureau of Animal Industry_.
The following list of parasites is prepared from the detailed host
catalogues of the zoological divisions of the Public Health and
Marine-Hospital Service and the Bureau of Animal Industry.
The species of hosts and parasites are taken as given by the various
authors. It is needless to say that no list of this kind can ever lay
claim to being complete.
Genus MUS Linneaus, 1758.
[_Mus musculus_ should be the type species.]
MUS AGRARIUS.—Harvest Mouse.
CESTODA:
_murina_ Dujardin: Hymenolepis.—Small intestine. [See fraterna.]
NEMATODA:
_obvelata_: Oxyuris.—Intestine.
ARACHNOIDEA:
_acuminatus_ Neumann: Ixodes.—External.
INSECTA:
_fasciatus_ Bosc: Ceratophyllus.—External.
_musculi_ Dugès: Ctenopsyllus, Ctenopsylla.—External.
MUS ALBIPES.
INSECTA:
_pallidus_ Taschenberg: Pulex.—External.
MUS ALEXANDRINUS.—Roof Rat.
[See also _Mus rattus alexandrinus_.]
CESTODA:
_diminuta_ Rudolphi, 1819: Tænia, Hymenolepis.—Small intestine.
_fasciolaris_ Rudolphi: Cysticercus.—Liver.
_leptocephala_: Tænia.—Small intestine.
_murina_ Dujardin: Hymenolepis.—Small intestine. [See fraterna.]
MUS ALEXANDRINUS ALBIVENTRIS.
CESTODA:
_diminuta_ Rudolphi: Hymenolepis.—Small intestine.
MUS AMPHIBIUS.
_Dubium_ Rudolphi.—Inguinal gland.
CESTODA:
_fasciolaris_ Rudolphi: Cysticercus.—Liver.
_omphalodes_ Hermann: Tænia, Anoplocephala.—Intestine.
NEMATODA:
_nodosus_: Trichocephalus.—Cecum.
_obvelata_: Ascaris.
MUS ARVALIS.
CESTODA:
_fasciolaris_ Rudolphi: Cysticercus.—Liver.
_longicollis_: Cysticercus.
_omphalodes_ Hermann: Tænia, Anoplocephala.—Intestine.
NEMATODA:
_nodosus_: Trichocephalus.
_obvelata_: Ascaris.
ACANTHOCEPHALA:
_moniliformis_: Echinorhynchus.
MUS BARBARUS.
[See also _barbatus_ Enderl.]
INSECTA:
_spiculifer_ Gerv.: Hæmatopinus, Polyplax.—External.
MUS BRASILIENSIS Geoffr.
[See also _Holochilus brasiliensis_.]
CESTODA:
_pisiformis_ Zeder: Cysticercus.
NEMATODA:
_muris brasiliensis_ Diesing: Physaloptera.
_obvelata_ Bremser: Oxyuris.
MUS CAPENSIS.
CESTODA:
_muris capensis_: Tænia.—Intestine.
NEMATODA:
_contortus_ Rudolphi: Trichocephalus.—Cecum.
MUS CRICETUS.
CESTODA:
_straminea_ Gœze: Tænia.—Intestine.
MUS DECUMANUS Pallas.—Brown or Norway Rat; German Wanderratte.
PROTOZOA:
? _balfouri_: Hæmogregarina.—Blood.
_intestinalis_ Lambl, 1859: Lamblia.—Intestine. [See duodenalis.]
_lewisi_ Saville-Kent: Herpetomonas, Trichomonas, Trypanosoma.—Blood.
species Siebold: Sarcocystis.—Muscles.
TREMATODA:
_armata_: Cercaria.
_muris_: Distomum.
_spiculator_ Dujardin, 1845: Distoma, Echinostoma, Distomum,
Echinostomum.—Small intestine.
CESTODA:
_brachydera_ Diesing: Tænia.—Small intestine.
_contracta_ Janicki: Hymenolepis.—Intestine.
_crassa_ Janicki: Hymenolepis.—Intestine.
_diminuta_ Rudolphi: Tænia, Hymenolepis.—Small intestine.
_fasciolaris_ Rudolphi: Cysticercus.—Liver.
_horrida_ Linstow, 1901: Tænia, Hymenolepis.—Intestine.
_microstoma_ Dujardin: Tænia, Hymenolepis.—Small intestine.
_murina_ Dujardin, 1845: Tænia, Hymenolepis.—Small intestine. [See
fraterna.]
_nana_ Siebold: Hymenolepis.—Small intestine. [See fraterna, murina.]
_pusilla_ Gœze: Tænia, Catenotænia.—Small intestine.
_ratti_: Tænia.—Intestine.
_relicta_ Zschokke, 1888: Tænia, Hymenolepis.—Small intestine.
species Janicki: Hymenolepis.
species: Hymenolepis.—Small intestine.
NEMATODA: