Bilharzia: A schistosome, a trematode worm parasite. Three main species of these worms'Schistosoma haematobium, S. japonicum, and S. mansoni'cause disease in humans. Larval forms of the parasite live in freshwater snails. When the parasite is liberated from the snail, it burrows into the skin, transforms to the schistosomulum stage, and migrates to the urinary tract (S. haematobium), or liver or intestine (S. japonicum or S. mansoni), where the adult worms develop. Eggs are shed into the urinary tract or the intestine, where they hatch to form another form of the parasite, called miracidia, that can then infect snails again, completing the parasite's life cycle. Also known as schistosomiasis.