Schistosome infection of snails in a dam traced to pollution with sewage

Abstract

The snail vectors of bilharziasis are freshwater forms preferring quiet pools and reservoirs to more rapid streams. Decreasing rainfall in Africa and increasing alternation of flood and aridity caused formation of many intermittent streams where water is often found only in natural or artificial pools. Here snails are numerous and pollution from human sources heavy. A larger proportion of snails become infested and more people use the water with increased risk of infecting themselves. The history of one such artificial reservoir showed that the incidence of infected snails was over 20 times that of the snails in a flowing stream.