Isozyme analysis with 18 enzyme loci was conducted on 146 isolates of Trypanosoma cruzi from Mexico, Guatemala, Colombia, Ecuador, Peru, Brazil, Bolivia, Paraguay and Chile. Forty-four different MLGs (groups of isolates with identical multilocus genotypes) were identified and a phylogeny was constructed. The phylogenetic tree consisted of two main groups (T cruzi I, T cruzi II), and the latter was further divided into two subgroups (T cruzi IIa, T cruzi IIb-e). Evidence of hybridization between different MLGs of T cruzi II was found, which means that genetic exchanges seem to have occurred in South American T cruzi. On the other hand, the persistence of characteristic T cruzi I and T cruzi II isozyme patterns in single small villages in Bolivia and Guatemala suggested that genetic exchange is very rare between major lineages. A significant difference in genetic diversity was shown between T cruzi I and T cruzi II from several indices of population genetics. Two possibilities could explain this genetic variation in the population: differences in evolutionary history and/or different tendencies to exchange genetic material. Broad-scale geographic distributions of T cruzi I and T cruzi IIb-e were different
T cruzi I occurred in Central America and south to Bolivia and Brazil, while T cruzi IIb-e occurred in the central and southern areas of South America, overlapping with T cruzi I in Brazil and Bolivia. (C) 2004 Elsevier Ireland Ltd. All rights reserved.