: infestation with or disease caused by schistosomes; specifically : a severe endemic disease of humans in much of Africa and parts of Asia and South America that is caused by any of three trematode worms of the genus Schistosoma (S. haematobium, S. mansoni, and S. japonicum) which multiply in snail intermediate hosts and are disseminated into freshwaters as furcocercous cercariae that bore into the body when it is in contact with infested water, migrate through the tissues to the visceral venous plexuses (as of the bladder or intestine) where they attain maturity, and cause much of their injury through hemorrhage and damage to tissues resulting from the passage of the usually spiny eggs to the intestine and bladder whence they pass out to start a new cycle of infection in snail hosts—called also bilharzia, bilharziasis, snail fever; compare swimmer's itch