Development of Schistosoma mansoni in the intermediate host Biomphalaria
glabrata is influenced by a number of parasite and snail genes.
Understanding the genetics involved in this complex host/parasite
relationship may lead to an often discussed approach of introducing
resistant B. glabrata into the field as a means of biological control for
the parasite. For the snail, juvenile susceptibility to the parasite is
controlled by at least four genes, whereas one gene seems to be responsible
for adult nonsusceptibility. Obtaining DNA from F2 progeny snails from
crosses between parasite-resistant and-susceptible snails, we have searched
for molecular markers that show linkage to either the resistant or
susceptible phenotype. Both restriction fragment length polymorphism (RFLP)
and random amplified polymorphic DNA (RAPD) approaches have been used. To
date, using a variety of snail and heterologous species probes, no RFLP
marker has been found that segregates with either the resistant or
susceptible phenotype in F2 progeny snails. More promising results however
have been found with the RAPD approach, where a 1.3 kb marker appears in
nearly all resistant progeny, and a 1.1 kb marker appears in all
susceptible progeny.