Host-parasite relationship of Bulinus truncatus and Schistosoma haematobium in Iran. 2. Effect of exposure dosage of miracidia on the biology of the snail host and the development of the parasites.

Laboratory experiments were carried out to study the development of Bulinus truncatus and the larval stages of Schistosoma haematobium after the snails had been exposed to various numbers of miracidia. The results showed: (1) that in the cercarial-incubation period the growth and survival rate of snails was not influenced by the development of the larval stages of S. haematobium, but that in the cercaria-shedding period the life-span of the infected snails was shorter than that of the non-infected controls; (2) that reduction of oviposition was proportional to the exposure of miracidia; (3) that the length of the cercarial-incubation period in snails was inversely proportional to the exposure number of miracidia; (4) that all the snails exposed to 20 miracidia (the maximum exposure number used) shed cercariae; (5) that snails exposed to one miracidium each shed fewer cercariae than those exposed to two or more miracidia each; and (6) that the peak of cercaria-shedding occurred 40 to 90 days after the shedding had started, varying in different groups.