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 $$N=254$$ 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 $$K = 3$$ K = 3 . These clusters are also easily identified in a neighbor-joining tree and principal coordinates plots. K-means analysis with $$K > 3$$ 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.

Evidence for local transmission and maintenance of schistosomiasis in an urban neighborhood in Northeast Brazil

“…The genetic distance of individuals from the group is another approach to evaluating whether parasites of immigrants largely originated outside of the Piraja community. We have shown that communities separated by 6 km on the same river can be distinguished by Dc (Blanton et al, 2011) and principal coordinate with k-means analysis of the Dic or Nei's genetic distance (Long et al, 2022). Using parasites of those born in Salvador as the component population, no clustering was observed by principal component (PCA) or network analyses (FigureS3).…”

Evidence for local transmission and maintenance of schistosomiasis in an urban neighbourhood in Northeast Brazil

“…The genetic distance of individuals from the group is another approach to evaluating whether parasites of immigrants largely originated outside of the Pirajá community. We have shown that communities separated by 6 km on the same river can be distinguished by Dc (Blanton et al., 2011) and principal coordinate with k‐means analysis of Dic or Nei's genetic distance (Long et al., 2022). Using parasites of those born in Salvador as the component population, no clustering was observed by principal component or network analyses (Figure S3).…”