Fig. 35.—Trypanosoma cruzi. Development in Triatoma megista. 1-6, forms found in the mid gut of Triatoma; 7 flagellate forms found in the posterior part of the gut of Triatoma. (After Chagas.)
Life History in the Invertebrate Host.—About six hours after the ingestion of infected blood by the bug (Triatoma megista), the kinetic nucleus of the trypanosome moves towards the nucleus, and the flagellum is usually lost (fig. 35, 1-5). The parasite becomes rounded and Leishmania-like (fig. 35, 3-5), and multiplies rapidly by division. After a time, multiplication having ceased, the rounded forms become pear-shaped and develop a flagellum at the more pointed end. Crithidial forms (fig. 35, 7) are thus produced and pass into the intestine, where they multiply and may be seen in about twenty-five hours after the ingestion of blood. The crithidial forms may also be found in the rectum and fæces. The last stage in the invertebrate is a small, trypanosome-like type, long and thin with a band-like nucleus and conspicuous kinetic nucleus. These parasites are found in the hind gut and in the body cavity. They find their way into the salivary glands, and are the forms (fig. 36) which are transmissible to a new vertebrate host. The development in the bug takes about eight days altogether, after which time the bugs are infective.
There are thus three principal phases in the development of T. cruzi in Triatoma megista: (1) A multiplicative phase (Leishmania-like) in the stomach of the bug, (2) a crithidial phase, which is also multiplicative, in the hind-gut, and (3) a trypanosome phase, which is “propagative,” and apparently passes through the wall of the alimentary canal into the body cavity and so into the salivary glands.
Fig. 36.—Trypanosoma cruzi. Forms found in the salivary glands of Triatoma megista. (After Chagas.)
Brumpt found that T. cruzi could live in Cimex lectularius, C. boueti, and Ornithodorus moubata. The Cimex fæces may be infective. Blacklock found multiplication of the parasite in C. lectularius.
Culture.—The trypanosome can be cultivated on Novy-MacNeal’s blood agar, and the cultural forms resemble those described in the bug.
Possible Reservoir.—Chagas thinks that probably the armadillo or “tatu” (Dasypus novemcinctus) may be the reservoir of T. cruzi. He also thinks that Triatoma geniculata is a transmitter; it lives in the burrows of the armadillo. Other carriers may be Triatoma infestans and T. sordida.
Clinical Features.—The trypanosomiasis of Brazil, produced by T. cruzi and spread by Triatoma spp. has received various names, such as oppilação, canguary, parasitic thyroiditis, and coreotrypanosis. It is also known as the human trypanosomiasis of Brazil, South American trypanosomiasis, and Chagas’ disease.
Chagas88 reports two principal forms—acute and chronic. The acute infection is rare, and is characterized by increase in the volume of the thyroid gland, pyrexia, a sensation of crackling in the skin, enlarged lymphatic glands in the neck, axilla, etc., while the liver and spleen are increased in volume. Sclerosis of the thyroid gland is found at autopsy and fatty degeneration of the liver. During an attack of fever, trypanosomes are found in the blood. The acute form was only observed in children.
In the chronic form Chagas reports several varieties: (a) A pseudo-myxœdematous form, occurring in most cases, especially up to the age of 15. There is hypertrophy of the thyroid gland or at least signs of hypothyroidism, general hypertrophy of glands, disturbance of heart rhythm, and nervous symptoms. (b) The myxœdematous form is characterized by similar symptoms, especially by considerable swelling of the thyroid body, and myxœdema of the subcutaneous cellular tissue; sometimes there is a true pachydermic cachexia. (c) In the nervous form there are motor disturbances, aphasia, disturbances of intelligence or signs of infantilism, athetosis of the extremities and idiocy. There are also paralytic symptoms of bulbar origin, disturbances of mastication, phonation and deglutition, and in some cases convulsive attacks. (d) The cardiac form, characterized by disturbance of the heart rhythm. In all these forms the parasite is found at autopsy in the nervous substance, brain, bulb and heart.
Vianna (1911)89 has studied the histopathology of the disease. Some of the chief points are: in the heart muscle destruction of the sarcoplasm, followed by interstitial myocarditis; in the central nervous system invasion of the neuroglia cells and inflammatory reaction; in the suprarenal capsule invasion of medulla or cortex; inflammatory reaction can also be seen in the kidneys, the hypophysis and thyroid gland.
Recently Chagas states90 that “schizotrypanosomiasis” has been found in a child 15 to 20 days old, and that Trypanosoma cruzi has also been found in a fœtus—the mother being infected with the trypanosome. The trypanosomiasis can, then, be transmitted hereditarily.
Trypanosoma lewisi, Kent, 1881.
The trypanosome has a nucleus somewhat displaced anteriorly, about one-third of the way from the anterior (flagellar) end of the body, a relatively straight edge to the undulating membrane, and a rod-shaped blepharoplast (fig. 37, A). It averages about 25 µ long and 1·5 µ broad.
Much attention has been devoted in recent years to the elucidation of the life history of the rat parasite, Trypanosoma lewisi. It is usually non-pathogenic to its host. It has been shown that the trypanosome can be transmitted from rat to rat by the rat-flea, Ceratophyllus fasciatus, and by Ctenocephalus canis (the so-called dog-flea). (See also p. 92). The flagellate may also persist, but doubtfully develop, in the rat-louse, Hæmatopinus spinulosus. These researches may now be summarized.
Fig. 37.—Trypanosoma lewisi, from rat’s blood. a, ordinary form; b, small form; c, d, stages in equal binary fission; e, elongate form (longocaudense type), resulting from division as seen in d; f, unequal binary fission; g, h, multiple fission into four and eight; i, small form; j, binary fission of small form; K, division rosette. × 2,000. (After Minchin and Thomson.)
Life Cycle in the Vertebrate Host.—After infection of a rat, the trypanosomes usually appear in the animal’s blood in five to seven days. This incubation period applies either to a natural or an artificial infection. The trypanosomes first observed in the rat’s blood are diverse in form (fig. 37), being small, medium and large in size. This diversity is explained by the rapid multiplication taking place. A trypanosome may divide by equal longitudinal fission (fig. 37, C, D), but more commonly multiple fission occurs (fig. 37, G, H), and is unequal. Rosette forms are produced, in which the parent form can be recognized by its long flagellum (fig. 37, H) and attached to it are daughter individuals, smaller in size, from which flagella are growing. Minchin and J. D. Thomson (1912) find that the daughter forms may be set free sometimes with a crithidia-like facies (fig. 37, I), the blepharoplast being anterior but near to the nucleus. The daughter forms, when set free, may themselves divide by binary or multiple fission, in the latter case forming rosettes (fig. 37, K). Rosette forms were described by Moore, Breinl and Hindle in 1908.
Lingard,