Evidence for Host-Induced Selection in Schistosoma mansoni

Publisher Website
Google Scholar
Abstract
A population of S. mansoni from Kenya was isolated in 1968 and subsequently passaged simultaneously through 2 different vertebrate hosts, baboons and mice. Recent electrophoretic studies demonstrated that genetic differences in the degree of polymorphism and in allele frequencies of polymorphic loci existed between S. mansoni populations from the 2 hosts. The importance of vertebrate host-induced selection against particular alleles is examined as the mechanism to account for the observed differences. A population of S. mansoni which originally had been passaged through baboons and subsequently passaged through murine hosts for 4 generations was studied. At least 20 infected snails served as the source of parasite for each mouse passage. Allele frequencies of 4 polymorphic loci were assessed for each generation using horizontal starch gel electrophoresis. All 4 polymorphic loci (PGM-2, MDH-2, MDH-1, PGI) showed a selective trend towards allele frequencies identical with that of a strain (from the same isolate) maintained in mice for 12 yr. Vertebrate host-induced selection probably results in a decrease in parasite variability due to loss of alleles as field isolates of S. mansoni are passaged in murine hosts. The use of non-human primate hosts maintains a higher level of parasite variability.