Seasonal abundance of trematode cercariae in Bulinus truncatus in a small focus of schistosomiasis in the Nile Delta.

Bulinus truncatus was most numerous from June to August, and echinostome cercariae, present in 19.3% of snails, were the most prevalent of the 4 types of trematode cercariae found. The echinostomes occurred throughout the year, other cercariae only in certain months. Double infections were uncommon. The findings suggest that echinostome cercariae exercise some biological control of Schistosoma haematobium in the area studied.