Trypanosoma cruzi is the etiological agent of Chagas disease. T. cruzi is a protozoan parasite with a complicated life cycle involving triatomid insects as vectors and infecting a variety of mammalian species including man.
Humans are infected when insect feces contaminated with trypano-mastigotes are involuntarily rubbed into a wound inflicted by the bite of the same insect. Congenital transmission and transmission by blood transfusion can also occur. After infection, flagellate forms of the parasite are found in the blood but rapidly change into rounded amastigotes as they enter the reticuloendothelial cells of the host. The parasite multiplies by binary fission at this stage and undergoes differentiation into flagellate forms which re-enter the blood. Trypanomastigotes are elongated structures which are infective for the insect host, where a new amastigote-trypanomastigote cycle follows. The complete cycle in the insect takes about two weeks and the insect is infective during the remainder of its lifetime.
Although T. cruzi is found in insects and vertebrates as far north as the United States, Chagas’ disease is prevalent only in South and Central America. The disease is associated with low socio-economic conditions, because the insect vectors flourish in the cracks of stone, adobe, and thatched houses.
Sero-epidemiological studies suggest that more than 65 million individuals are infected and that the incidence of infection exceeds 50% in endemic areas. However, only about 10% of those infected develop the clinical picture characteristic of Chagas’ disease. Since T. cruzi can readily be recovered from the blood only in the acute phase, the need for an accurate serologic test is apparent.