Public health impact of schistosomiasis: disease and mortality. WHO Expert Committee on the Control of Schistosomiasis.

The public health significance of schistosomiasis is often underestimated for two reasons. First, like all helminthic infections, the distribution of worms in any community is widespread but uneven, i.e., few have heavy infections and severe disease, while many have lighter infections and fewer symptoms. Some people with very few worms may have no symptoms. Secondly, severe disease usually follows after many years of silent or mildly symptomatic infection. Even if only 10% of those 200 million infected with schistosomiasis have severe clinical disease, this still represents 20 million seriously ill people. Of the remaining 180 million infected people, an estimated 50-60% also have symptoms--a public health problem of enormous proportions. The impact on public health can be assessed in terms of the frequency and severity of schistosomiasis-related disease, incapacity and premature death. This article presents extracts from the Expert Committee's recently published second report and deals with morbidity and mortality, as well as the links between schistosomiasis and cancer, nutrition and intercurrent infections, and the immune response to schistosomiasis.