The effect of exposure to Schistosoma mansoni on mortality rates of cohorts of different ages of Biomphalaria pfeifferi.

The effect of exposure to miracidia of Schistosoma mansoni Sambon on mortality rates of five different age-groups of Biomphalaria pfeifferi (Krauss) was investigated under carefully controlled conditions in the laboratory. The per capita mortality rates were determined for each age-group and the mean life expectancy and mean snail mortalities per week calculated. It was demonstrated that the cohorts of snails exposed to three miracidia per snail at an age of one week suffered the highest mortalities during the prepatent period and had the shortest life-span. No significant differences could be indicated in these respects between cohorts of snails exposed at an age of three, four and five weeks to the same number of miracidia. The results of this investigation could make a significant contribution towards establishing and maintaining laboratory cultures of S. mansoni.