Host-parasite relationship of Bulinus truncatus and Schistosoma haematobium in Iran. 3. Effect of water temperature on the ability of miracidia to infect snails.

Laboratory studies were made in Iran to test the effect of water temperature on the ability of the miracidia of S. haematobium to penetrate B. truncatus. Snails three to four weeks old were exposed to two miracidia each for two hours at nine water temperatures ranging from 10 degrees C to 38 degrees C. After exposure, all the snails were kept in aquaria at room temperature. The cercaria-positive rates of these nine groups of snails showed that the optimum exposure temperature was in the range 20 degrees C-30 degrees C. The infection rate was low at temperatures outside this range. It is concluded that the optimum transmission seasons in bilharziasis-endemic areas in Iran are spring and autumn but that transmission still occurs in hot summer and cold winter months although to a much smaller extent.