International Conference on Molecular Epidemiology and Evolutionary Genetics of Infectious Diseases edition:10 location:Amsterdam date:3-5 November 2010
The parasitic flatworm Schistosoma spp. affects more than 200 million people worldwide and is responsible for the neglected tropical disease schistosomiasis. This chronic disease is characterized by a focal and complex epidemiology, which is still not fully understood. The use of molecular data provides insights into the distribution of parasite genotypes among hosts and is therefore essential to understand disease epidemiology. We therefore assessed the genetic diversity within and between natural S. mansoni populations in Northern Senegal. More than 1000 parasite stages (miracidia, cercariae and eggs) were collected from snails and human faeces within the villages Pakh, Diokhor and Thiekene. Individual samples were genotyped using nine multiplexed microsatellite loci. F-statistics revealed a random parasite distribution (panmixis) when individuals were used to define subpopulations. In addition, we found significantly lower allelic richness and lower expected heterozygosity for parasite populations within children than those within adults. These results confirm the idea that human hosts function as ‘genetic mixing bowls’, accumulating parasite strains during their lives. Parasite populations within adults are therefore more heterogenous than those within children. Interestingly, cluster analysis revealed a marked genetic differentiation between clusters without any prior boundary definition. Although the exact determinants of these clusters remain to be elucidated, it could be correlated with the number and spatial connectivity of the various parasite transmission foci. We will discuss our results in the light of the possible implications of parasite population genetic structure on schistosome epidemiology.