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 C57B l/6 (B6) and the susceptible C3H (He) mouse strains and compared to in fection with the known virulent Brazil strain. C3H mice were capable o f surviving acute Guayas infection, whereas the Brazil infection was f atal for this mouse strain. Both C3H and B6 mice showed a greatly redu ced (over Id-fold) parasitemia during Guayas infection compared to Bra zil infection. Histologic examination of heart tissue from Guayas-infe cted B6 and C3H mice indicates little inflammation, unlike what is typ ically seen in B6 mice chronically infected with the Brazil strain. Th ere appears to be no remarkable difference in the anti-parasite antibo dy 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, pr ovides an infection that generates a low parasitemia and strong anti-p arasite responses in the absence of specific anti-heart autoimmunity a nd obvious myocarditis. In vitro infection characteristics of these 2 parasite strains were studied in cultures of macrophages, myocytes, an d fibroblasts by microscopic examination of stained slide cultures. In both short-term (24 hr) and long-term (15 day) experiments, Brazil st rain infection was shown to have a greater infection rate with a highe r number of parasites per cell than Guayas infection for all host cell types. There was no indication of different tissue tropisms in that b oth parasite strains showed an equivalent ability to infect myocytes a nd macrophages. Determination of trypomastigotes released by infected cells into culture medium indicated that the intracellular reproductiv e cycle is shorter for the Brazil strain (7-12 days) than that of the Guayas (12-15 days). The more aggressive in vitro infection displayed by Brazil parasites compared to Guayas organisms may be the cause for the more virulent characteristics seen in Brazil-infected mice.