Genetic studies on variation in infectivity of Schistosoma mansoni.

Biomphalaria glabrata snails of known genetic susceptibility types were exposed to miracidia from 2 strains of Schistosoma mansoni differing in infectivity.. Individual snails were exposed to single miracidia and penetration observed. Snails of a genetic type susceptible to both parasite strains served as controls, while snails of a genetic type susceptible to one parasite strain but relatively refractory to the other served as test snails to demonstrate the difference in parasite infectivity. Cercariae from snails with single sex infection of each of the 2 parasite strains were injected into mice to provide crosses. Results of test snail exposures to F1 miracidia from reciprocal crosses suggested that the parasite strain difference in infectivity was genetic and involved sex linkage. Results also suggested that the female S. mansoni was heterogametic (XY), the male XX.