Host-parasite relationship of Bulinus truncatus and Schistosoma haematobium in Iran. 4. Effect of month of infection on cercarial-incubation periods of S. haematobium and S. bovis.

Studies were conducted each month for one year to determine the cercarial-incubation periods of Schistosoma haematobium and Schistosoma bovis in Bulinus truncatus for different months of infection. The snails were kept in outdoor aquaria in order to simulate the natural temperature conditions in the endemic bilharziasis areas of Iran.The results showed that the cercarial-incubation periods of these two schistosome species varied with the environmental water temperature. Snails exposed in August had the shortest incubation period, and snails exposed in November the longest. The cercarial-incubation period for S. haematobium was longer than that for S. bovis in all months. The difference between the cercarial-incubation period of these two species varied from three to 18 days, being greater in the winter than in the summer.It has been concluded that the low temperature of the water in the winter retards the development of miracidia into cercariae and that the winter is therefore the poorest season for potential transmission. In summer, in spite of the hot weather, snails may still shed cercariae, but spring and autumn are the optimum seasons for cercariae transmission.