Schistosomiasis, also known as bilharzia or “snail fever”, is a parasitic disease carried by fresh water snails infected with one of the five varieties of the parasite Schistosoma.
Schistosomiasis is due to immunologic reactions to Schistosoma eggs trapped in tissues. Antigens released from the egg stimulate a granulomatous reaction involving T cells, macrophages, and eosinophils that results in clinical disease.
Seroprevalence studies indicate that more than 90 percent of persons residing in high-risk transmission zones will acquire Schistosoma infection at some point in their lives, usually in the first decade of life. In areas of lower transmission risk from 25 up to 40 percent of individuals experience schistosomiasis by the age of 35.