Schistosoma mansoni: Continuous variation in susceptibility of the vector snail of schistosomiasis, Biomphalaria tenagophila - I. Self-fertilization-lineage

Artificial selection of Biomphalaria tenagophila snails for susceptibility to infection by Schistosoma mansoni (Brazilian SJ strain) was carried out f rom natural populations. After five self-fertilization generations, two lin eages were isolated and were designated as SUSC (highly susceptible 93-100% ) and RES (nonsusceptible 5-0%). Length of the prepatent period, cercarial production, and mortality of the hosts in postexposure were determined in a ll generations (F-1-F-8) and were analyzed as quantitative traits related t o host susceptibility. Distribution patterns of frequencies were observed w ithin snail families (samples derived from one F-0 snail), these traits sho wing a significant influence by selection applied to susceptibility. The mu ltiple quantitative classes were described in terms of continuous variation . During the selection of SUSC lineage, classes with higher values of prepa tent length and lower cercarial production were eliminated, and the heritab ility calculated for these two traits was 0.811 and 0.709, respectively Exp erimental results were correlated with an increase in the level of suscepti bility in the generations selected and are discussed in relation to inherit ance patterns as well as the quantitative variation of susceptibility. (C) 1999 Academic Press.