Blood Trematodes: Schistosomiasis

Schistosomiasis (i.e., bilharzia or snail fever) is a parasitic infection caused by trematodes that reside in the circulatory system. More than 230 million people worldwide suffer from schistosomiasis, which causes a range of clinical disease from overt clinical manifestations to subtle hindrance of day-to-day activities. Infected children can have impaired growth and development. Infection occurs from exposure to freshwater into which snails, the intermediate host of the parasite, have shed cercariae that can penetrate skin. The three main species of schistosomes that parasitize humans are Schistosoma mansoni, S. japonicum, and S. haematobium. Gastrointestinal and hepatic disease is caused by infection with S. mansoni or S. japonicum, and urogenital tract disease results from S. haematobium infection. Other schistosome species less commonly infect humans, including S. intercalatum, which is found in Cameroon and the Democratic Republic of Congo, and S. mekongi, which is found primarily in the Mekong River basin. Both species cause gastrointestinal disease.