Infection characteristics of an Ecuadorian Trypanosoma cruzi strain with reduced virulence.

A human isolate of Trypanosoma cruzi obtained from Guayaquil, Ecuador (Guayas strain) was examined for its infectivity of the resistant C57Bl/6 (B6) and the susceptible C3H (He) mouse strains and compared to infection with the known virulent Brazil strain. C3H mice were capable of surviving acute Guayas infection, whereas the Brazil infection was fatal for this mouse strain. Both C3H and B6 mice showed a greatly reduced (over 10-fold) parasitemia during Guayas infection compared to Brazil infection. Histologic examination of heart tissue from Guayas-infected B6 and C3H mice indicates little inflammation, unlike what is typically seen in B6 mice chronically infected with the Brazil strain. There appears to be no remarkable difference in the anti-parasite antibody responses (as measured by ELISA and western blot) in mice infected 100 days with Guayas or Brazil parasites. Western blot analysis of the anti-heart response indicates no response during Guayas infection to a 43-kDa heart tissue glycoprotein that is a target of antibodies from B6 mice infected with Brazil strain. The Guayas strain, therefore, provides an infection that generates a low parasitemia and strong anti-parasite responses in the absence of specific anti-heart autoimmunity and obvious myocarditis. In vitro infection characteristics of these 2 parasite strains were studied in cultures of macrophages, myocytes, and fibroblasts by microscopic examination of stained slide cultures. In both short-term (24 hr) and long-term (15 day) experiments, Brazil strain infection was shown to have a greater infection rate with a higher number of parasites per cell than Guayas infection for all host cell types.(ABSTRACT TRUNCATED AT 250 WORDS)