Genetic filtering and optimal sampling of Schistosoma mansoni populations

Allelic variation in 6 microsatellite markers was compared between frozen Schistosoma mansoni eggs and laboratory-passaged worms originating from the same 5 fecal samples obtained from Brazilian residents. Based on allelic richness values, the number of alleles detected per locus did not differ between egg and worm DNA templates. However, our ability to score loci differed between these DNA templates, with worms providing more scored loci per individual than eggs. Differences also existed between the worms and eggs in the identity of the specific alleles that were detected. Additionally, we observed a reduction in homozygous genotypes among laboratory-passaged worms relative to the eggs. Allelic diversity curves were calculated by genotyping all worms from a representative host sample to determine the relationship between the number of alleles detected at a locus and the number of worms genotyped. Curves for the 5 residents' worm infrapopulations for each of the loci were very similar. The equation y=19.55 x ln(x) + 9.992 explained the association between sampling effort (x) and number of alleles detected (y) with an R(2) of 0.775. In conclusion, egg DNA templates and allelic diversity curves can benefit efforts to discern the sociological, ecological and evolutionary forces impacting the genetic diversity and disease epidemiology of human schistosomes.