Abstract
Bulinus truncatus is the main intermediate host for Schistosoma haematobium in Egypt. The fates of Schistosoma miracidia in the snails varies between different populations of B.truncatus. The internal defense system is one of the factors that influence the susceptibility pattern of the snails. The interaction between Bulinus snail and S. haematobium need to be identified for each population, and even between the members of the same population with different degrees of susceptibility. In the present study, the first generation of B. truncatus collected from Giza and Damietta in addition to Schistosome Biological Supply Center (SBSC) was examined histologically at the 5week post exposure. The study includes the characterization of the immune response, as expressed by tissue reactions and hemocytes count of B. truncatus snail against S.haematobium. The results showed that the experimental snail groups were classified as follows: moderate susceptibility [SBSC (42.1%) and Damietta (39.4%)] and low susceptibility [Giza (17.85%)]. These results characterized the immune response of B. truncatus snail against Schistosoma infection which was found to occur by two different mechanisms. The results showed that granulocytes were present in significant greater number in all samples as compared to hyalinocytes (p<0.001). Exposure of B. truncatus to S. haematobium caused gradual increase in the number of circulating hemocytes in the three experimental groups. The variations in the rates of infection and immune response of different B. truncatus groups with S. haematobium, are dependent on collection site of the snails. Introduction of this variability into endemic areas may reduce the ability of the parasite to infect local hosts and consequently reduce schistosomiasis epidemiology.