Susceptibility of Bahian population of Biomphalaria glabrata to an allopatric strain of Schistosoma mansoni.

Seventeen populations of snails (Biomphalaria glabrata) from the state of Bahia, Brazil were studied with respect to their susceptibility to infection with an allopatric strain of Schistosoma mansoni. Two of the populations were from the city of Salvador, 3 from other sites in Bahia, and 12 from habitats in the municipio Castro Alves. Our data show that the Bahian snail populations are extremely variable in their susceptibility to an allopatric strain of S. mansoni and that the phenomenon is not associated solely with distantly separated strains, but is present, as well, in adjacent populations situated in a restricted geographic region. Of the 6 populations found to be completely refractory to infection when exposed at a size of 5--7 mm, only 2 were refractory when exposed at 5--12 days of age. It is suggested that the variability to infection displayed by populations in a restricted geographic area may be explained by assuming that the Founder Principle was operative.