Trypanosoma cruzi - Agent of American trypanosomiasis. Chaga's Disease
T. cruzi infects humans and a wide variety of domestic and wild species. It is a major human health problem in South America, especially Brazil, Venezuela, and Argentina. Transmission depends on the presence of the parasite, vectors, reservoirs, and the host being present in the same location. Vectors are kissing bugs of the genus Triatoma and Rhodnius. Important reservoir animals in the U.S. are raccoons, opossums, and armadillos.
Once infected, trypomastigotes appear in peripheral blood in 2 to 3 weeks. Amastigotes (above) can cause cardiomyopathy resulting from muscle fiber damage by toxic parasite products, cardiac adrenergic destruction or autoimmune-mediated mechanisms. Clinically, the acute form is characterized by lymphadenomegaly. Acute myocarditis is not uncommon. Common signs include pale mucous membranes, a slowed capillary refill time, weak pulse, tachyarrhythmia, and terminal hypothermia and respiratory distress. Dogs that do not die develop ascites and hepatomegaly due to right side heart failure. Anorexia and diarrhea are also common. Neurologic signs including weakness and ataxia, suggesting distemper, are also common. ECG changes during the acute phase are variable. During the asymptomatic period between the acute and chronic phase of infection, ECG may be normal except for intermittent ventricular arrhythmia, often exacerbated by exercise. Sudden death can occur due to fatal cardiac arrhythmia. As cardiac dilation occurs, ECG abnormalities become more prevalent and clinical signs referable to right-sided and eventually left-sided chamber failure occur. Trypanosomiasis should be considered in any dog with signs of myocarditis or cardiomyopathy.
Felines are reported to be susceptible to infection but little is known of clinical disease in this species.
Diagnosis is dependent on detecting trypomastigotes in peripheral blood films, lymph node aspiirates or impression smears, or isolation in susceptible laboratory animals or cell culture. Trypomastigotes are most common in peripheral blood during and just prior to the acute phase, being less common in the chronic phase. Serology (IFA, CF, DH) is routinely used to detect chronic infections.
Treatment is effective with nifurtimox, although it is not approved in the U.S. Treatment with anti-inflammatory doses of glucocorticoids and other supportive measures are useful.
Trypanosoma theileri- Apparently a non-pathogenic parasite of cattle in the U.S. Vector(s) are not known.
Trypanosoma cervi - A non-pathogenic parasite of deer and other cervids in the U.S. Horseflys are suspected as vectors.