Relationships between histopathological findings and phylogenetic divergence in Trypanosoma cruzi

Problems have been raised by natural genetic diversity of Trypanosoma cruzi, the causal agent of Chagas' disease, and other protozoa in terms of both basic and applied science. T. cruzi manifests a great diversity of medical and biological properties which could be the origin of clinical variability in the disease. We propose possible correlations between genetic distances, or phylogenetic divergence, and histopathological data. To ascertain this aspect, 15 cloned stocks pertaining to three major clones or genotypes (19, 20 and 39) were compared. Sets of 24 mice infected with each stock were studied for histopathological lesions. Brain, heart, lung, liver, spleen, urinary bladder, bone marrow, colon, kidney and skeletal muscle were extracted from each mouse. Qualitative and quantitative differences showed at histopathological examination. An important encephalic softening was found in brains of most mice infected by genotype 20, corresponding to areas of inflammation and liquified necrosis. Other inflammatory tissue lesions in the histological sections of the three genotypes were similar. Skeletal muscle tropism was higher than cardiac tropism in all the studied genotypes. All three genotypes shared parasite presence in skeletal muscle. Differences related to cardiac tropism were important: in genotype 19, 50% of studied stocks presented pseudocysts; 20% in genotype 20 and 83% in genotype 39. Parasite presence in other tissues was scanty: in brain only in genotype 20 and in spleen and liver only in genotype 39. We found important histopathogenicity differences among the three studied genotypes, but they do not support the hypothesis of zymodeme pathogenic specificity due to the great diversity among stocks within each genotype.