Authors

Discussion

The
epidemiology of schistosomiasis in northern Senegal is changing. Schistosoma mansoni was the dominant
parasite at the onset of the epidemic in the early nineties, but has nowadays
in many places been overtaken by the urinary species S. haematobium. Moreover, molecular analyses revealed that children
were infected with S. haematobium x S. bovis hybrids, the latter being a
livestock parasite. Here we want to compare the population genetic structure of
the two main schistosome species and their respective snail host species in
order to understand the role of vector co-adaptation, colonization history and hybridization
on schistosome transmission dynamics.

Our
results revealed limited S. haematobium gene
flow between the Middle Valley and the other regions in Northern Senegal, as is
the case for one of the bulinid snail hosts. This contrasts with the panmictic
population structure found for both S.
mansoni and the snail host B.
pfeifferi. We discuss this contrasting resultin relation to the presence and genetic constitution of the
intermediate snail hosts, and the colonisation history of the parasites.

We
found no evidence that hybridization influenced the genetic make-up of S. haematobium populations in Senegal. Human schistosomes with a S. bovis mitochondrial haplotype could
not be differentiated from schistosomes with a S. haematobium mitochondrial haplotypeas revealed by 17 nuclear microsatellite markers. In addition, no
first generation hybrids were found. This suggests limited gene flow between
human and cattle parasite populations, and that hybridization does not lead to
a barrier breakdown between both species in this area.