rat. It has been taken in this country on mice. It lives at the base of
the hairs.
_Myobia ensifera_ Poppe.
This was described from the brown rat in Europe. The female is separated
from _M. musculi_ by having about six of the posterior dorsal spines
flattened and scale like; in the male the six dorsal spines are longer,
and the small spines much smaller than in _M. musculi_.
SARCOPTIDÆ.
These are the itch and scab mites. The body is soft, rounded, and
whitish in color. The legs are very short, of five joints, and end in
one or two claws, and often a pediceled sucker. The palpi are small and
short, of three joints, but the basal is usually united to the rostrum.
There are no spiracles, and respiration is therefore through the general
surface of the skin. The sexes are often quite different in structure.
The females usually deposit eggs, the larvæ are hexopod, and there are
two nymphal stages. They are all parasites, mostly on mammals and birds,
and often burrow in the skin, causing mange, or scabies.
Only one species has been taken on rats; this belongs to the genus
_Notoedres_.
_Notoedres._—In this genus the third pair of legs of the male and the
third and fourth of the female have no sucker at the tip. The anal
opening is on the posterior part of the dorsum. The three known species
are parasitic on mammals—one on the cat, one on the rabbit, and the
third on rats.
_Notoedres muris_ Mègnin.
This is a rounded mite, with finely striate skin, a small triangular
rostrum; in front the four anterior legs project a little beyond the
body, and each ends in a long pedicellate sucker; the third and fourth
pairs of legs are not visible from above, and each ends in a long
bristle. There are a few short hairs around the anal aperture and about
ten others in front of these. The species measures about 0.3 to 0.4
millimeter long.
It usually occurs about the ears and the genital organs of the host, and
has been taken from both the brown and black rat in Europe. The
_Sarcoptes alepis_ Railliet and Lucet is the same species.
DEMODECIDÆ.
Besides the mites above described, a form of _Demodex_ has been recorded
from rats, but the species is not given. These mites are very tiny, with
elongate body, the posterior part annulate, the front part with eight
very short legs. They inhabit the hair follicles of various mammals.
That on the rat may have been only an accidental occurrence of some
species normally on another animal.
THE INTERNAL PARASITES OF RATS AND MICE IN THEIR RELATION TO DISEASES OF
MAN.
By CH. WARDELL STILES, _Chief_, and CHARLES G. CRANE, B. S., _Assistant,
Division of Zoology, Hygienic Laboratory, United States Public Health
and Marine-Hospital Service_.
SUMMARY.
Rats and mice may harbor 11 species of internal parasites which come
into consideration as possible or established parasites of man. From
this point of view, 7 of the parasites are of more academic interest
than practical importance. The rat may, however, be viewed as the
practical, theoretical, and permanent reservoir for one zooparasitic
disease (trichinosis) of considerable importance, and of at least one,
perhaps two, other zooparasitic infections (“_Lamblia duodenalis_” and
_Hymenolepis diminuta_) of much less importance. Its possible future
rôle in connection with sleeping sickness should not be entirely
ignored.
From the standpoint of internal zooparasitism, therefore, the present
public health interest in rats and mice centers in trichinosis. This
disease will probably never be eradicated from man until rats and mice
are practically eradicated, and any rational public health campaign
directed against trichinosis must take the rat into serious
consideration.
The eradication of rats and mice would be a very substantial
contribution toward a reduction and eradication of trichinosis.
INTRODUCTION.
From the habits of rats, it is to be expected that they harbor many
species of parasites, and on account of their presence in our houses the
question naturally arises as to whether any of these parasites are
transmissible, either directly or indirectly, to man.
The species of internal parasites which come especially into
consideration in this connection are the following:
PROTOZOA: _Chlamydophrys enchelys_ (p. 88), _Lamblia duodenalis_ (p.
89), _Trypanosoma gambiense_ (p. 94).
TREMATODA: None.
CESTODA: _Cysticercus cellulosæ_ (p. 95), _C. fasciolaris_ (p. 96),
_C. pisiformis_ (p. 95), _H. murina_ Duj. [= _fraterna_] (p. 96),
_Hymenolepis diminuta_ (p. 98).
NEMATODA: _Trichinella spiralis_ (p. 101).
ACANTHOCEPHALA: _Gigantorhynchus moniliformis_ (p. 108).
ARACHNOIDEA: _Linguatula denticulata_ (p. 110).
Of these 11 species, the trichina worm (sometimes called the flesh worm)
exceeds all the others combined, both in frequency and importance, as a
cause of disease in man.
PROTOZOA.
Genus CHLAMYDOPHRYS[U] Cienkowski, 1876.
Footnote U:
SYNONYM.—_Leydenia_ Schaudinn, 1896.
Species CHLAMYDOPHRYS ENCHELYS[V] (Ehrenberg.)
Footnote V:
SYNONYMS.—_Difflugia enchelys_ Ehrenberg; _Chlamydophrys stercorea_
Cienkowski; _Leydenia gemmipara_ Schaudinn, 1896; _Chl. enchelys_
(Ehrenberg) Braun.
A very peculiar organism has been described under the name of _Leydenia
gemmipara_ Schaudinn, 1896. This was found in fluid, obtained by
puncture, from two ascites patients in Berlin, Germany. More recently
Schaudinn has concluded that _Leydenia gemmipara_ represents an abnormal
condition of a protozoon known as _Chlamydophrys_. The latter passes
through the intestinal tract of various animals (as man, mice,
squirrels, rabbits, cattle), and thus is occasionally found in fresh
human stools. According to Schaudinn, if pathological conditions in the
colon cause an alkaline reaction of its entire content, the usual shell
formation in _Chlamydophrys_ fails to take place, the organisms then
multiply in an atypical manner by division and budding, and the result
is the structure described as _Leydenia gemmipara_.
Genus LAMBLIA[W] R. Blanchard, 1888.
Footnote W:
SYNONYMS.—_Dimorphus_ Grassi, 1879 (not Haller, 1878, arachnoid);
_Megastoma_ Grassi, 1881 (not de Blainville, mollusk; not Swains.,
1837, bird; not Costa, 1850, fish; not Megerle, mollusk); “_Dimorpha_
Grassi” of Senn, 1901 (not _Dimorpha_ Jur., 1807, hymenopteron; not
Gray, 1840, mollusk; not Hodgs., 1841, bird); _Megastroma_
Schneidemuehl, 1898, misprint.
GENERIC DIAGNOSIS.—_Polymastigidæ_: Body bilaterally symmetrical,
pyriform, excavate antero-ventrally to form a sucker; flagella
directed posteriorly; 3 pairs inserted on margin of the sucker, 1 pair
at posterior end of body. Parasitic in intestine of mammals.
TYPE SPECIES.—_Lamblia duodenalis_ s. l. (“_L. intestinalis_” of man).
Flagellate protozoa belonging to this genus are reported as parasitic in
the intestinal canal of various species of mammals. At present the forms
in question are usually looked upon as belonging to the species _L.
duodenalis_. Evidence is, however, accumulating (p. 92) to the effect
that there are at least three distinct species of _Lamblia_ (“_L.
intestinalis_” of man, _L. muris_ of mice, and _L. cuniculi_ (or
_duodenalis_?) of rabbits). Admitting that there may be three species,
the intertransmissibility of these forms from one host to another
remains to be investigated to some extent. It seems thus far definitely
proved that the form which occurs in man is transmissible to mice,
rabbits, and guinea pigs, hence mice still remain a source of danger in
respect to the infection in man. To exactly what extent this fact is of
academic interest or of practical significance is at present _sub
judice_.
Species LAMBLIA DUODENALIS[X] (Davaine, 1875) Stiles, 1902, s. l.
Footnote X:
SYNONYMS.—_Cercomonas intestinalis_ Lambl, 1859, in man (not _Bodo_
(_Cercomonas_) _intestinalis_ (Ehrenberg, 1838) Diesing, 1850, in
frogs; not _Cercomonas intestinalis_ (Ehrenberg, 1838) Perty, 1852);
_Hexamita duodenalis_ Davaine, 1875, in rabbits; _Dimorphus muris_
Grassi, 1879, in _Mus_; _Megastoma entericum_ Grassi, 1881 (=
_Dimorphus muris_ renamed); _Megastoma intestinale_ (Lambl, 1859) R.
Blanchard, 1885; _Lamblia intestinalis_ (Lambl, 1859) R. Blanchard,
1888; “_Megastoma intestinalis_” of Leclerq, 1890; “_Cercomonas
intistinalis_ Lambl” of L. Pfeiffer; “_Megastroma entericum_ Grassi,
1881” of Schneidemuehl, 1898; “_Dimorpha muris_ Grassi” of Senn, 1900.
[Figs. 9 to 15.]
SPECIFIC DIAGNOSIS.—_Lamblia_ (p. 88): Body pyriform, 5 to 16μ (21μ
Lambl) long, 4 to 12.5μ (8.6 to 11μ Lambl) broad; flagella 9 to 14μ
long; anterior end bluntly rounded, posterior end sharply pointed,
dorsum convex, antero-ventrally concave, venter flat to convex;
antero-ventral concavity forms a sucker, the margins of which project
from the surface and are contractile. Four pairs of ventral
posteriorly directed flagella, arranged as follows: 1 pair insert on
anterior margin of sucker; 2 pairs on posterior margin of sucker, near
median line; 1 pair on posterior extremity. Body membrane (“cuticula”)
very delicate, permitting some change of body form; protoplasm finely
granular; nucleus dumb-bell shaped, pre-equatorial. Vacuoles not
observed. Copulation sucker-to-sucker, followed by an encystation, in
which stage complicated nuclear changes occur; cysts 10 by 7μ.
HABITAT.—Upper portion of small intestine of man (_Homo_); also of the
common house mouse (_Mus musculus_), the brown rat (_M. decumanus_),
the black rat (_M. rattus_), “_Mus sylvestris_” [=? _M. decumanus_],
field mouse (_Microtus arvalis_), water mole (_Arvicola amphibius_),
rabbits, guinea pigs, domesticated cats, dogs, and sheep.
GEOGRAPHICAL DISTRIBUTION.—Europe, Egypt, and United States.
This parasite is very common in animals in certain parts of Europe, and
cases of its presence in man have been reported by a number of authors
(Lambl, 1859; Grassi, 1881; Perroncito, 1888; Moritz, 1891; Moritz &
Holzl, 1892; Roos, 1893; Kruse & Pasquale, 1894; Piccardi, 1895;
Sievers; Mueller; Frshezjesski & Ucke; Stiles, 1902; Braun, 1908; etc.).
The indications are that it is more common in man than is generally
assumed.
Possibly man becomes infected through eating food (as bread, etc.) which
has been soiled by the excrements (containing the encysted stage) of
mice and rats. Grassi infected himself, Perroncito infected mice and
rabbits, and Stiles infected guinea pigs by feeding to them human feces
containing the encysted stage.
The parasite may be present in large numbers. Moritz estimated a
discharge of 18 milliards within twenty-four hours from one of his
patients. It has been observed in healthy persons and also in cases of
various diseases, but especially in children and in cases of
tuberculosis. It is an inhabitant chiefly of the duodenum and jejunum,
where it attaches itself (fig. 13) by means of the sucker to the
epithelial cells. It is rarer in the ileum. In case the stomach is
alkaline (carcinoma) the parasite may occur in this organ (Cohnheim,
Zabel). In P. Schmidt’s case the hydrochloric acid was 1 per cent. In
case the intestinal peristalsis is normal the parasite becomes encysted
in the colon, so that usually only the encysted stage is found in the
feces; but in case of increased peristalsis and diarrhea the organisms
have not time to encyst, so that the free stages are observed in the
stools. As the parasites become cool motion decreases; when raised to
high temperature, as 50° C., motion becomes slow, and the organisms die
at 52° C. or below 0° C.
[Illustration:
FIG. 9.—Lateral view of encysted _Lamblia duodenalis_.
FIG. 10.—Cyst from large intestine.
FIG. 11.—Ventral view of _Lamblia_.
FIG. 12.—Lateral view.
FIG. 13.—Epithelial cells of the villous coating of the small
intestine infested with _Lamblia_. (After
Grassi & Schewiakoff, 1888, pl. 15, figs. 1, 2, 5, 11, 12.)
]
[Illustration:
FIG. 14.—An epithelial cell with parasitic _Lamblia_. Greatly
enlarged. (After Grassi & Schewiakoff, 1888, pl. 15, fig. 6.)
]
[Illustration:
FIG. 15.—An individual in the act of joining an epithelial cell.
(After Grassi & Schewiakoff, 1888, pl. 15, fig. 7.)
]
PATHOGENICITY.—Opinion differs as to the pathogenicity of this organism.
Perroncito (1902b) reports it as causing a fatal disease in rabbits.
Braun (1908) is inclined to consider it harmless. From conversation with
Doctor Hemmeter, we are persuaded that in his case in a child in
Baltimore the parasite was not without effect. Possibly the question as
to its pathogenicity is a relative one in that light infections may
produce no recognizable disturbance, while heavy infections may produce
recognizable effects. Doctor Hemmeter’s original letter regarding his
case contained the following notes:
Patient, male, white child, 3 years old, born in Maryland. Had
recurrent attacks of colitis all its life; three acute attacks within
the last three weeks, accompanied by fever, distended abdomen,
sensitive, etc. Stools have always been like putty, containing large
amount of mucus, and some blood streaks; fever lasting three days, no
pronounced diarrhea, 2 to 3 passages per day; intervals between
attacks variable, stools at such times like putty, also with mucus.
Later information from Doctor Hemmeter states that the disappearance of
the parasites from the stools coincided with improvement in the child’s
condition.
CLINICAL DIAGNOSIS.—The fresh unstained stools should be examined
microscopically; or the diluted stool may be stained with methylene
blue, by which nearly all objects become promptly stained, except
_Lamblia_, which remains grayish white (Roos, 1893) for several hours.
TREATMENT.—Attempts to expel _Lamblia_ have not always met with marked
success. Among the drugs used are male fern, sulphate of quinine,
naphthol, calomel, hydrochloric acid, and arsenic. Grassi appears to
have had success with calcined magnesia.
[Illustration:
FIG. 16.—“_Lamblia intestinalis_” of man. (After Bensen, 1908, fig.
5.)
]
[Illustration:
FIG. 17.—Copulation cyst of “_Lamblia intestinalis_” of man. (After
Bensen, 1908, fig. 5.)
]
THE DIVISION OF _Lamblia duodenalis_ INTO SEPARATE SPECIES.—Bensen
(1908) has recently divided _Lamblia duodenalis_ s. l. into three
species: _L. “intestinalis,”_ _L. muris_, and _L. cuniculi_. His
preliminary paper seems to offer fairly convincing data for the
correctness of his interpretation, but it may be well to await the
publication of his more complete paper, in which he promises fuller
details, before the species are definitely accepted. Several
nomenclatural points will come up for consideration in this connection.
_Lamblia intestinalis_, which Bensen accepts as name for the species
(fig. 16) occurring in man, can not be accepted, as this name is based
on _Cercomonas intestinalis_ Lambl, 1859, which is invalidated by
_Cercomonas intestinalis_ (Ehrenberg, 1838) Perty, 1852, found in frogs.
_Lamblia muris_ (fig. 18) will probably stand, based on _Dimorphus
muris_ Grassi, 1879.
_Lamblia cuniculi._—There is some doubt as to the status of this name.
Davaine (1875a, 128–129) has described from rabbits a protozoon, which
he designated as _Hexamita duodenalis_ and which Railliet (1893a, 169)
identifies as a synonym of _Lamblia intestinalis_ (Lambl). On basis of
the principle that identifications are to be accepted as correct until
shown to be incorrect, Stiles has accepted _duodenalis_ as name (1902)
for the form in question. The question now arises as to the relation of
_cuniculi_ to _duodenalis_. If they are accepted as identical,
_duodenalis_ will supplant _cuniculi_, and a new name must be given to
the form found in man. If _duodenalis_ is taken as identical with
_intestinalis_ Lambl, _duodenalis_ remains as name for the form in man,
and _cuniculi_ Bensen will stand for the species in rabbits. If
Railliet’s interpretation of synonymy be shown to be incorrect by
proving that _duodenalis_ Davaine is not to be considered in connection
with either form, a new name must be given to _intestinalis_ Lambl.
[Illustration:
FIG. 18.—_Lamblia muris_ of mice. (After Bensen, 1908, fig. 1.)
]
[Illustration:
FIG. 19.—Autogametocyte of _Lamblia muris_. (After Bensen, 1908, fig.
6.)
]
Genus TRYPANOSOMA s. l.
An extensive group of parasitic protozoa, known as “trypanosomes,” has
recently been the basis of considerable literature. The genus
_Trypanosoma_ was originally based upon a species (_T. rotatorium_)
found in frogs, and while most trypanosomes have been described as
members of this genus several authors have separated out certain forms
into separate genera.
Luehe (1906) has recently placed the trypanosomes of mammals in the
Genus TRYPANOZOON Luehe, 1906.
One of these species (_Trypanozoon gambiense_, usually known as
_Trypanosoma gambiense_) is the cause of “sleeping sickness” in man, and
has been transmitted in laboratory experiments to rats and mice.
[Illustration:
FIG. 20.—An isolated pork-measle bladder worm (_Cysticercus
cellulosæ_), with extended head. Greatly enlarged. (After Stiles,
1898a, 90, fig. 76.)
]
Just what practical importance there may be in the ability of the
parasite to live in rats and mice remains to be seen, but theoretically
this biological factor may possibly become one of considerable
magnitude. At present the least conclusion to be drawn is that it adds
one more to the many arguments in favor of a world-wide destruction of
rats and mice.
Several trypanosomes, other than _Trypanozoon gambiense_, are
transmissible by experiment to rats and mice, while one species
(_Trypanozoon lewisi_) has rats for its normal host, and two other
species (_Trypanozoon duttoni_ and _Trypanosoma musculi_ Kendall, 1896)
are reported originally from the mouse.
CESTODA—TAPEWORMS.
Of the five cestodes mentioned as coming into consideration in the
subject under discussion, only one (_Hymenolepis diminuta_) need be
considered seriously.
CYSTICERCUS CELLULOSÆ—TÆNIA SOLIUM.
[Fig. 20.]
The larval cestode known as _Cysticercus cellulosæ_ (which causes
“measles” in swine) develops (when eaten by man) into a tapeworm which
is known as _Tænia solium_. This larva is also reported as encysted in
the peritoneum of _Mus rattus_.
[Illustration:
FIG. 21.—Portion of mesentery of rabbit infected with _Cysticercus
pisiformis_. Natural size. (After Railliet, 1893a, 216, fig. 114.)
]
Even if it be granted that the specific determination of the specimen in
question as _Cysticercus cellulosæ_ is correct, the occasional infection
of rats with this parasite would be of very little practical
significance in this country from a public health point of view, as we
do not use rats for food for man. Theoretically it is possible to
conceive of combinations of circumstances in which such infection in the
rat might under certain conditions eventually affect man, but the
chances are so remote as to be negligible, especially when compared with
the much greater questions which demand attention.
CYSTICERCUS PISIFORMIS—TÆNIA PISIFORMIS.
[Fig. 21.]
The larval stage of this parasite occurs in rabbits, the adult stage in
canines. Parona (1901) reports the occurrence of the larval stage in
_Mus brasiliensis_, and Vital has recorded the presence of the adult
stage in man.
In view of the fact that Galli-Valerio was unable to infect himself
experimentally with this species, the specific determination made by
Vital is open to some question. Even assuming that this tapeworm may
develop in man, the presence of the larval stage in rats is of such
little importance as to be negligible.
CYSTICERCUS FASCIOLARIS—TÆNIA TENIÆFORMIS.
[Fig. 22.]
This encysted larval tapeworm is exceedingly common in the liver of rats
and mice, and when swallowed by cats it develops into an adult tapeworm.
[Illustration:
FIG. 22.—Larval stage of _Tænia teniæformis_. Natural size. (After
Leuckart, 1880, 450, fig. 202.)
]
There are two possible points of view in connection with which this
parasite is of indirect interest in public health matters: (1)
Occasionally these encysted parasites are mistaken for lesions of
tuberculosis; (2) Krabbe (1880) relates that in Jutland there exists a
folk custom of eating chopped raw mice in case of retention of urine,
and in this connection the point has been raised that the possibility is
not excluded that such action might eventually give rise to infection of
man by the parasite in question. No case of such infection in man is as
yet established.
HYMENOLEPIS MURINA[Y] (Dujardin, 1845) = HYMENOLEPIS NANA FRATERNA[Y]
Stiles, 1906.
Footnote Y:
SYNONYM.—_Tænia murina_ Dujardin, 1845 (not Gmelin, 1790).
[Figs. 23 and 24.]
Under the name _Tænia murina_, Dujardin (1845) described for rats a
tapeworm which has been identified by a number of authors (including
Stiles) as identical with the dwarf tapeworm (_Hymenolepis nana_) of
man. If this identification be correct, the rats must be considered as
the great disseminators of this tapeworm. Serious doubts have been
raised, however, as to whether the tapeworm in man is not in reality
distinct from that of the rat, and the evidence in favor of such
conclusion is accumulating. Some slight differences between the two
forms have been noticed, but by some authors these differences have been
considered insufficient to hold the two worms apart. Looss has tried to
infect rats with the dwarf tapeworm found in man in Egypt, but his
results have been negative. Here in Washington Stiles has repeatedly
attempted to infect rats with the dwarf tapeworm found in man in the
United States, but thus far no positive infection has occurred in the
rodents. In Italy, Grassi attempted to transmit the rat form to six
persons, and in one case he found tapeworms, but in view of the
frequency of _H. nana_ in Italy the significance of this one instance
has been questioned; Grassi was not successful in trying to infect rats
with _H. nana_ of man.
[Illustration:
FIG. 23.—Longitudinal section of the intestinal villus of a rat,
containing cystic stage of dwarf tapeworm. Enlarged. (After Grassi &
Rovelli, 1892a, pl. 3, fig. 25.)
]
[Illustration:
FIG. 24.—Adult dwarf tapeworm (_Hymenolepis nana_) of man. Enlarged.
(After Leuckart, 1863, p. 393, fig. 112.)
]
Thus at present the evidence is to the effect that rats and mice are not
to be viewed as the source or reservoir for the dwarf tapeworm (_H.
nana_) of man.
HYMENOLEPIS DIMINUTA[Z] (Rudolphi, 1819) R. Blanchard, 1891.
Footnote Z:
SYNONYMS.—_Tænia diminuta_ Rudolphi, 1819; _T. leptocephala_ Creplin,
1825; _Hymenolepis flavopunctata_ Weinland, 1858; _Tænia (Hymenolepis)
flavopunctata_ Weinland, 1859; _H. (Lepidotrias) flavopunctata_
Weinland, 1861; _T. flavomaculata_ Leuckart, 1863; _T. “flavopuncta”_
Cobbold, 1864 (misprint); _T. “flaviopunctata”_ Vogt, 1878 (misprint);
_T. “flavopunktata”_ Stein, 1882; _T. varesina_ E. Parona, 1884; _T.
minima_ Grassi, 1886; _T. “septocephala”_ Perroncito and Airoldi, 1888
(misprint); _Hymenolepis diminuta_ (Rudolphi, 1819) Blanchard, 1891;
_“Hymenolepsis” flavopunctata_ of Osler, 1895, and other authors
(misprint); _T. “varerina”_ Huber, 1896 (misprint for _T. varesina_);
_T. “flavapunctata”_ Simon, 1896 (misprint); _T. “leptocefala”_
Previtera, 1900; _T. “ceptocephala”_ Lussana and Romaro [? date]
(misprint); _Tenia flavopunctata_ (Weinland, 1858) Packard, 1900.
[Figs. 25 to 30.]
[Illustration:
FIG. 25.—Strobila of _Hymenolepis diminuta_. Natural size. (After
Grassi, 1881, pl. 11, fig. 1.)
]
[Illustration:
FIG. 26.—Head and anterior portion of _H. diminuta_ from the rat.
Enlarged. (After Zschokke, 1889, pl. 1, fig. 21.)
]