Cryptic population structure and transmission dynamics uncovered for Schistosoma mansoni populations by genetic analyses

Abstract

Patterns of diversity in pathogen genomes provide a window into the spatiotemporal spread of disease. In this study, we tested the hypothesis that Schistosoma mansoni parasites form genetic clusters that coincide with the communities of their human hosts. We also looked for genetic clustering of parasites at the sub-community level. Our data consists of 14 microsatellite DNA markers, typed from pooled DNA samples from $N=254$ infected individuals living in three Brazilian communities. We found a one-to-one correspondence between genetic clusters found by K-means cluster analysis and communities when $K=3$. These clusters are also easily identified in a neighbor-joining tree and principal coordinates plots. K-means analysis with $K>3$ also reveals genetic clusters of parasites at the sub-community level. These sub-clusters also appear on the neighbor-joining tree and principal coordinates plots. A surprising finding is a genetic relationship between subgroups in widely separated human communities. This connection suggests the existence of common transmission sites that have wide influence. In summary, the genetic structure of S. mansoni in Brazil juxtaposes local isolation that is occasionally broken by long-range migration. Permanent eradication of schistosomes will require both local efforts and the identification of regional infection reservoirs.