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 show 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 co-existing 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 show 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 showing recovery in population after "Winter Closure" later than Bulinus, Biomphalaria and Physa. Helisoma proved to be free of any natural trematode infection.