| Schistosoma mansoni is one of the most widespread and abundant parasites of humans in Africa, Madagascar, Arabia, South America, and the Antilles, and it requires freshwater snails of the genus Biomphalaria as intermediate hosts for its larval stages.; The most comprehensive phylogenetic analysis of Biomphalaria to date (23 species), including the most important S. mansoni hosts, was completed based on nuclear ITS1, ITS2, and mtDNA 16S nucleotide sequences, and the results suggest a New World origin for the genus and that African species are derived. African species formed the sister clade of Biomphalaria glabrata, which suggests they shared a common ancestor that colonized Africa in the Pliocene and also explains why B. glabrata is such an important host. Susceptibility to S. mansoni is found in both basal and derived parts of the Biomphalaria tree, and the ability of S. mansoni to adapt to New World Biomphalaria is significant.; Nucleotide sequences (mitochondrial 16S and ND1; nuclear ITS1 and actin intron I) were utilized to examine the historical phylogeography of the two most important intermediate host species of S. mansoni: B. glabrata in the New World, and B. pfeifferi in the Old World. Mitochondrial sequences were informative and showed that Biomphalaria glabrata is a species with highly differentiated populations, as indicated by 6 mitochondrial clades, which were isolated in the Pleistocene. Some of these clades in Brazil have come to have geographically overlapping ranges. Biomphalaria pfeifferi is much less divergent (4X less), consistent with the previous phylogenetic study, and the oldest populations were from southeast Africa.; Mitochondrial sequences (ND1) and eight microsatellite loci were used to examine the genetic diversity of Schistosoma mansoni isolates in the New World, including isolates which infect alternative intermediate hosts to B. glabrata, or which infect rodents instead of humans. Mitochondrial diversity was very low in the New World, consistent with the hypothesis that S. mansoni has occurred there only since the slave trade. Microsatellites were variable among and within populations, but no strong patterns of differentiation were seen in isolates using alternative hosts, especially in rodent- vs. human-isolates, which had very low levels of divergence. |
