schistosomiasis

schistosomiasis (bilharzia) Any one of a group of diseases of humans and some other Mammalia caused by infestation by blood flukes (Trematoda of the genus Schistosoma). The trematode requires two hosts; the first is an aquatic snail in which larvae emerging from eggs hatched in water develop through several stages, finally to fork-tailed forms (cercariae) which escape from the snail, swim freely in the water, and attach themselves to, and penetrate, the skin of their second host, a mammal. In the mammalian body they move through blood vessels, feeding upon glycogen in the blood plasma and growing, eventually migrating to a site that varies from species to species, where they mature, mate, and lay eggs. The eggs leave the body in urine or faeces. Symptoms vary according to the species causing the infestation, but may include swelling and tenderness of the liver, dropsy, enlargement of the spleen, watery skin eruptions, fever, cough, haemorrhage, diarrhoea, and reduced function of the affected organs. The diseases are common in low latitudes.