BIOLOGICAL CHARACTERIZATION OF TRYPANOSOMA-CRUZI STOCKS FROM CHILEAN INSECT VECTORS

Fifty-seven Trypanosoma cruzi stocks isolated from Triatoma infestans and Triatoma spinolai of the five different geographic endemic areas o f Chile were studied by schizodeme and molecular karyotype analysis. F our different genotypes are found in the sylvatic I spinolai vector an d five in the T. infestans domiciliary vector. Of these genotypes, two common genotypes overlap on both transmission cycles exclusively in t he extreme northern endemic areas of Chile. Metacyclic trypomastigotes obtained in vitro or cell-derived trypomastigotes proved to be infect ive in gamma-irradiated Balb/c mice for the study of the immune respon se and biological behavior. Of a total of 57 T. cruzi stocks obtained, 19 of them, representing all the different genotypes found in Chile, were tested on a murine experimental model and then fully studied. Fem ale compared with male animals demonstrated greater resistance to Chag as disease with all the T. cruzi stocks tested. The immune response wa s assessed by lytic antibodies that were studied by the in vitro antib ody-dependent complement-mediated lytic assay with the use of bloodstr eam trypomastigotes as target cells. In one unique parasite genotype t he elicited lytic antibodies reacted in a genotype-specific manner, in contrast with lytic antibodies generated by other T. cruzi genotypes. Parasitemias were high, moderate, and low, with mortality ranges of 6 -50%, 0-45%, and 0-10%, respectively. No association was found between specific infective genotypes and virulence or mortality. Independentl y of the T. cruzi strain studied, each population displayed a characte ristic parasitemia curve and prepatent period. A considerable number o f the parasite stocks proved to be mixed populations, according to mol ecular karyotype patterns obtained before and after differentiation an d amplification of the parasites. This fact created difficulty in asse ssing the identity of the genotype really infective to mice. (C) 1998 Academic Press.