T. cruzi can be spread from animals to man and back again through the bites of the kissing bug. Generally the reservoir hosts such as dogs and cats do not show signs of the infection. In dogs, however, weakness, anemia and an enlarged spleen and lymph nodes may develop in severe infections. Rarely, if large numbers of the parasite entered the heart, an inflammation of the heart may occur and the dog may suddenly collapse and die. In others, the diseased heart may fail slowly and could be confused with more common types of heart disease.
Some dogs show profound weakness and incoordination.
Cats may have convulsions and paralysis of the hind limbs. If a large number of the host's cells rupture at the same time, fever may occur. In Africa, another species of trypanosomes causes African sleeping sickness that is spread by the tsetse fly. This is a very serious disease in South and Central America. In the acute phase, people have fever, lethargy, and enlarged lymph nodes and spleens.