Part 9

_Lælaps stabularis_ Koch.

The body is of the same general shape as in _L. echidninus_, but the dorsum is clothed with 12 to 18 rows of fine short hairs. The first pair of legs is more slender than in the other species, and the hind legs are also more elongate; the coxæ do not have the stout spines seen in the other species, and the bristles on the sternal and ventral plates are much less stout; the general surface of the venter has many hairs, the anal plate has a short apical bristle. Length, 1.2 millimeters.

Taken on the brown rat in Italy; also found in manure.

CHEYLETIDÆ.

This family consists of small, soft-bodied mites, that are parasitic or predaceous in habits. The palpi are small, three or four jointed; the mandibles are styliform and retractile; and the breathing spiracles open near the mouth parts. The species that occur on rats belong to the genus _Myobia_.

_Myobia._—The body is elongate, fully twice as long as broad, tipped by a pair of long, stout bristles. The first pair of legs is enlarged and shortened, with a terminal hook to grasp hairs; the other legs are short, simple, and far apart. The palpi and mouth parts are very small, and the dorsum bears stout bristles. They are supposed to feed on the exudations of the skin, but it would seem more probable, from the nature of the mandibles, that they pierced the skin to secure food. All are very small, not one-half a millimeter long. Of the several species two have been recorded from rats.

1. Dorsum of female with spines all acute and sharp _M. musculi_.

Dorsum of female with some of the posterior spines flattened and rather scale like _M. ensifera_.

_Myobia musculi_ Schrank.

This occurs on various mice and moles, and once recorded from the brown 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.) ]