British Society for Parasitology Spring Meeting location:Bristol date:8-11 April 2013
Environmental change and increasing movements of people and animals lead to species introductions into new areas. In the case of parasitic organisms, the successful establishment of an introduced parasite species depends largely on the life cycle. Parasites with a complex life cycle, for instance, need one or more intermediate host species in order to establish successfully. About thirty years ago, two dams were constructed in the Senegal River Basin in order to improve the agricultural conditions in Northern Senegal. The subsequent ecological changes stimulated the spread of Bulinus and Biomphalaria snail species, intermediate hosts of the human parasites Schistosoma haematobium and S. mansoni, respectively. Both parasite species could rapidly colonize northern Senegal following the massive population expansion of their intermediate snail hosts and the increasing human immigration for agriculture. While S. mansoni colonization was characterized by an explosive spread, S. haematobium expansion occurred more slowly. This is a unique system where the origin of an epidemic outbreak is exactly known, providing an opportunity to study the molecular evolution of pathogens in a relative short time frame. We therefore assessed the genetic variability at microsatellite loci within and between natural populations of S. mansoni and S. haematobium in several villages along several waterways in northern Senegal. F- and R-statistics revealed a tenfold higher genetic differentiation between S. haematobium populations than between S. mansoni populations. As the level of human host mobility is the same for both parasite species, these results can either be explained by (or a combination of) a difference in the level of snail host mobility and/or by a different demographic history of the snail host or the parasite itself. Various demographic and genealogical histories will therefore be explored using MCMC simulation programs.