The population structure of Trypanosoma cruzi: Expanded analysis of 54 strains using eight polymorphic CA-repeat microsatellites

Recently we cloned and sequenced the first eight Trypanosoma cruzi polymorp hic microsatellite loci and studied 31 clones and strains to obtain valuabl e information about the population structure of the parasite. We have now s tudied 23 further strains, increasing from 11 to 31 the number of strains o btained from patients with chronic Chagas disease. This expanded set of 54 strains and clones analyzed with the eight microsatellites markers confirme d the previously observed diploidy, clonal population organization and very high polymorphism of T. cruzi. Moreover this new study disclosed two new f eatures of the population genetic structure of T. cruzi. The first was the discovery that, similarly to what we had previously shown for strains isola ted from insect vectors, mammals and humans with acute disease, isolates fr om patients in the chronic phase of Chagas disease could also be multiclona l, albeit at a reduced proportion. Second when we used parsimony to display the genetic relationship among the clonal lineages in an unrooted Wagner n etwork we observed like before, a good correlation of the tree topography w ith the classification in three clusters on the basis of single locus analy sis of the ribosomal RNA genes. However, a significant new finding was that now the strains belonging to cluster 2 split in two distant sub-clusters. This observation suggests that the evolutionary history of T. cruzi may be more complex than we previously thought.