Schistosoma monsoni (Puerto Rican strain) cercariae were exposed to 10, 20, 50, 100, 200, 300, 400 and 500 krad gamma radiation from “Co gamma source. From 10-100 krad irradiation no differences could be found in the behaviour of the cercariae when compared to the controls. From 200-500 krad there was an increase in mortality as well as in the number of cercariae that shed their tails. The Con A binding studies also performed on cercariae radiated with up to 100 krad indicate a direct relationship between the number of cercariae that bind Con A and radiation dose. All live cercarial heads collected after radiation also bound Con A. It thus seems possible that irradiation may act as a stimulus for cercariae to transform to schistosomulae.
The effect of exposure to miracidia of Schistosoma mansoni Sambon on mortality rates of five different age-groups of Biomphalarìa 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.