Genetic diversity and population structuring of Schistosoma mansoni in a Brazilian village.

The digenean trematode Schistosoma mansoni is responsible for chronic schistosomiasis worldwide, and in Brazil alone an estimated 35 million people are at risk. To evaluate epidemiological patterns among human definitive hosts, we assessed genetic diversity and population subdivision of S. mansoni infrapopulations in human hosts from the highly endemic village of Virgem das Graças in the state of Minas Gerais, Brazil. We believe this is the largest such survey to date. Genetic diversity of parasites, measured over eight polymorphic microsatellite loci, was relatively high and standard measures of inbreeding indicated that the population was panmictic. Furthermore, there was no significant isolation-by-distance of parasite infrapopulations, and measures of population subdivision indicated significant but low to moderate levels of population differentiation. We conclude that patients within this village sample from a broad range of schistosome genetic diversity and effectively act as "genetic mixing bowls" for the parasites. These results contrast with those previously observed in the Brazilian village of Melqui ades and thus provide the opportunity for comparisons of environmental and epidemiological differences that are likely to influence host-parasite coevolution and parasite transmission.