Characterization of Trypanosoma cruzi.

The Trypanosoma cruzi is a heterogeneous population, composed by a pool of strains which circulate in both the domestic and sylvatic life cycles including humans, vectors and animal reservoirs. Isolation and study of T. cruzi populations from different origins demonstrated the presence of a large range of strains with distinct biological, immunological, biochemical and pharmacological characteristics. Studies using cloned or uncloned T. cruzi populations, reinforce the heterogeneity of the parasite and demonstrate that the strains are composed of subpopulations with distinct characteristics (Postan et al. 1986, Finley & Dvorak 1987). Morphological differences in the T. cruzi blood forms have already been described by Chagas in 1909 in his classical paper on the discovery of Chagas disease (Chagas 1909). The role of the slender and broad bloodstream forms trypomastigotes were later thoroughly studied by Brener (1973). Nussenzweig et al. (1963) and Nussenzweig and Goble (1966) described immunological differences among T. cruzi strains. The strains were divided into three groups according to their cross-reaction with heterologous serum from infected mice. Following these biological and immunological observations, new approaches have been used for molecular characterization of T. cruzi. Enzyme electrophoresis studies have demonstrated distinct T. cruzi populations (zymodemes) circulating in the domestic and sylvatic transmission cycles and provided a good epidemiological marker for Chagas disease. Miles et al. (1977, 1978) studying T. cruzi strains isolated from the Brazilian states of Bahia and Pará, described the