Also known as BILHARZIASIS. This infection is common in Africa, South America, the Far East, Middle East, and, to a limited extent, the Caribbean. It is caused by Schistosoma worms. The adult male is about 12 mm and the female 24 mm in length. Fresh-water snails act as a host for schistostoma, which enter via intact human skin and mature in the PORTAL SYSTEM. ‘Swimmers’ itch’ may occur at the site of acute schistosomiasis (see KATAYAMA FEVER) resulting in fever, an urticarial rash (see URTICARIA), and enlargement of LIVER and SPLEEN.

S. haematobium causes CYSTITIS and haematuria – passage of blood in the urine; bladder cancer and ureteric obstruction, giving rise to hydronephrosis and kidney failure, are long-term sequelae in a severe case. S. mansoni can cause colonic symptoms and in a severe case, POLYPOSIS of the COLON with bloody diarrhoea. In a heavy infection, eggs surrounded by granulomas are deposited in the liver, giving rise to extensive damage (pipe-stem fibrosis) associated with PORTAL HYPERTENSION. Diagnosis can be made by microscopic examination of URINE or FAECES. The characteristic eggs are usually detectable. Alternatively, rectal or liver BIOPSY is of value. Serological tests, including an ELISA, have now largely replaced invasive procedures previously used in making a parasitological diagnosis.