Schistosoma mansoni is the most widespread of the human-infecting schistosomes, present in 54 countries, predominantly in Africa, but also in Madagascar, the Arabian Peninsula, and the Neotropics. Adult-stage parasites that infect humans are also occasionally recovered from baboons, rodents, and other mammals. Larval stages of the parasite are dependent upon certain species of freshwater snails in the genus Biomphalaria, which largely determine the parasite's geographical range. How S. mansoni genetic diversity is distributed geographically and among isolates using different hosts has never been examined with DNA sequence data. Here we describe the global phylogeography of S. mansoni using more than 2500 bp of mitochondrial DNA (mtDNA) from 143 parasites collected in 53 geographically widespread localities. Considerable within-species mtDNA diversity was found, with 85 unique haplotypes grouping into five distinct lineages. Geographical separation, and not host use, appears to be the most important factor in the diversification of the parasite. East African specimens showed a remarkable amount of variation, comprising three clades and basal members of a fourth, strongly suggesting an East African origin for the parasite 0.30-0.43 million years ago, a time frame that follows the arrival of its snail host. Less but still substantial variation was found in the rest of Africa. A recent colonization of the New World is supported by finding only seven closely related New World haplotypes which have West African affinities. All Brazilian isolates have nearly identical mtDNA haplotypes, suggesting a founder effect from the establishment and spread of the parasite in this large country.

BackgroundWe investigated changes in the spatial distribution of schistosomiasis in Mali following a decade of donor-funded control and a further 12 years without control.Methodology/Principal FindingsNational pre-intervention cross-sectional schistosomiasis surveys were conducted in Mali in 1984–1989 (in communities) and again in 2004–2006 (in schools). Bayesian geostatistical models were built separately for each time period and on the datasets combined across time periods. In the former, data from one period were used to predict prevalence of schistosome infections for the other period, and in the latter, the models were used to determine whether spatial autocorrelation and covariate effects were consistent across periods. Schistosoma haematobium prevalence was 25.7% in 1984–1989 and 38.3% in 2004–2006; S. mansoni prevalence was 7.4% in 1984–1989 and 6.7% in 2004–2006 (note the models showed no significant difference in mean prevalence of either infection between time periods). Prevalence of both infections showed a focal spatial pattern and negative associations with distance from perennial waterbodies, which was consistent across time periods. Spatial models developed using 1984–1989 data were able to predict the distributions of both schistosome species in 2004–2006 (area under the receiver operating characteristic curve was typically >0.7) and vice versa.Conclusions/SignificanceA decade after the apparently successful conclusion of a donor-funded schistosomiasis control programme from 1982–1992, national prevalence of schistosomiasis had rebounded to pre-intervention levels. Clusters of schistosome infections occurred in generally the same areas accross time periods, although the precise locations varied. To achieve long-term control, it is essential to plan for sustainability of ongoing interventions, including stengthening endemic country health systems.

The historical phylogeography of the two most important intermediate host species of the human blood fluke Schistosoma mansoni, B. glabrata in the New World, and B. pfeifferi in the Old World, was investigated using partial 16S and ND1 sequences from the mitochondrial genome. Nuclear sequences of an actin intron and internal transcribed spacer (ITS)-1 were also obtained, but they were uninformative for the relationships among populations. Phylogenetic analyses based on mtDNA revealed six well-differentiated clades within B. glabrata: the Greater Antilles, Venezuela and the Lesser Antilles, and four geographically overlapping Brazilian clades. Application of a Biomphalaria-specific mutation rate gives an estimate of the early Pleistocene for their divergence. The Brazilian clades were inferred to be the result of fragmentation, due possibly to climate oscillations, with subsequent range expansion producing the overlapping ranges. Within the Venezuela and Lesser Antilles clade, lineages from each of these areas were estimated to have separated approximately 740 000 years ago. Compared to B. glabrata, mitochondrial sequences of B. pfeifferi are about 4x lower in diversity, reflecting a much younger age for the species, with the most recent common ancestor of all haplotypes estimated to have existed 880 000 years ago. The oldest B. pfeifferi haplotypes occurred in southern Africa, suggesting it may have been a refugium during dry periods. A recent range expansion was inferred for eastern Africa less than 100 000 years ago. Several putative species and subspecies, B. arabica, B. gaudi, B. rhodesiensis and B. stanleyi, are shown to be undifferentiated from other B. pfeifferi populations.

Snail surveys were carried out in various parts of Mali . All areas surveyed are part of the Niger basin being either affluents or irrigation schemes fed by this river . The snail species present varied greatly between areas .The following potential hosts of schistosomes were recorded : Biomphalaria pfeifferi, Bulinus truncatus, B, globosus, B. umbilicatus, B. forskalii and B. senegalensis.In the large irrigation schemes, i .e. `Office du Niger' and Baguineda, only B, pfeifferi and B. truncatus appear to be intermediate hosts . Snail distribution appeared to some extent to be focal and high snail densities appeared to be associated with human water contact activities, which apparently create favourable biotopes for the snails . This is probably due to an alteration of the vegetation and an increase of the trophic status of the site by contamination with food remnants and other debris . The larger irrigation canals or lakes in these schemes play an important role in the transmission of human schistosomes and transmission appears to be very focal in these habitats . Infected snails are almost exclusively found in well-defined human water contact sites (WCS) . Local infection rates with schistosomes were often high (i .e. up to 27% in B, pfeifferi) .In urban areas (i .e. Bamako), transmission patterns are more variable . In Bamako schistosome-infected B.truncatus were found in the Niger river . A number of smaller semi-permanent or permanent streams are very important transmission sites, and schistosome infections were recorded from B. pfeifferi, B. truncatus and B. globosus. Schistosome infection rates in B. pfeifferi were often high (up to 30%).In a new lake at Selingue, B. truncatus was found to be widely distributed only about a year and a half after the dam was constructed, and in some sites schistosome infections were recorded .