Helisoma duryi: its present range of distribution and implications with schistosomiasis snails in Egypt

The range of distribution of Helisoma duryi, a potential competitor to schistosomiasis snail vectors in Egypt, was determined in the south of Nile Delta. Results showed that H. duryi was found in the River Nile, Geziret El-Kerateyeen banks, Damietta and Rosetta Branches, Tawfiky and Menoufy Canals and their branches and Bassoussiya, Bahadiya and Sheshaa Canals and their branches. Helisoma was found in all categories of canals and drains coexisting in various degrees with other snail species including schistosomiasis vectors [Bulinus truncatus and Biomphalaria alexandrina]. The population density of H. duryi and associated B. truncatus, B. alexandrina and Physa acuta were studied for one year in three channels. Statistical analysis of results showed that Helisoma has a significantly negative correlation with schistosomiasis vectors in these channels. Helisoma population showed a major peak in the warmest months of the year [July-August], thus showed recovery in population after "Winter Closure" later than Bulinus, Biomphalaria and Physa. Helisoma proved to be free of any natural trematode infection

effect of temperature on inter-relationship between schistosoma haematobium and bulinus truncatus in Egypt

The prepatent period, death rate, infection rate and cercarial production of S. haematobium in B. truncatus maintained under different constant temperatures were studied. The cercarial production varied greatly in infected snails at different constant temperatures. It varied from 874.65 to 23.5. The highest cercarial output was in snails kept at 25°C and the lowest at 18°C. Some infected snails maintained at 19°C, 25°C and 28°C discharged cercariae for more than ten weeks from their first shedding

Prepotency of schistosoma haematobium in snails at different constant temperatures

The developmental time of Schistosoma haematobium in Bulinus truncatus was determined at different constant temperatures between 18°C and 32°C. The basic relationship between the length of the minimum prepatent period [Y, in days] and the temperature [X, in°C] is given by the hyperbolic formula Y = 295 / [X-15.3], 15.3 being the theoretical [developmental null point] and 295 the constant time-temperature product. The epidemiological application, the prognosis of the transmission period and the estimation of the transmission potential in relation to climatic conditions are discussed