Schistosomiasis, also known as bilharzia or snail fever, is a parasitic disease caused by blood flukes that live in freshwater snails. The larval form of the parasite, called cercariae, emerges from the snail and contaminates water. People become infected when their skin comes into contact with the contaminated water. Treating water sources with chemicals to kill snails (molluscicides) can reduce the number of infective larvae.This will help control the snails.