SCHISTOSOMIASIS

Disease of liver, gastrointestinal tract and bladder caused by trematode worms that parasitize people. The infection is acquired from infested water. Three main species of these trematode worms (flukes)--Schistosoma haematobium, S. japonicum, and S. mansoni—cause disease in humans. Larval forms of the parasite live in freshwater snails. The cercaria (form of the parasite) is liberated from the snail burrow into skin, transforms to the schistosomulum stage, and migrates to the urinary tract (S. haematobium), liver or intestine (S. japonicum, S.mansoni) where the adult worms develop. Eggs are shed into the urinary tract or the intestine and hatch to form miracidia (yet another form of the parasite) which then infect snails, completing the life cycle of the parasite. Adult schistosome worms can seriously damage tissue. Schistosome species which cannot live in man cause swimmer’s itch. Schistosomiasis is also called bilharzia after the shortlived German physician Theodor Bilharz (1825-1862)