Schistosomiasis (Bilharzia)

Schistosomiasis is due to infection with blood flukes and is contracted through skin or mucosal contact with infected water.

Infective agent is a fluke: S.mansoni, S.haematobium or S.Japonicum.

Distribution: Africa, South America, and less so in the Middle and Far East.

Personal prevention measures: Avoid skin contact with fresh water in endemic areas. eg. ponds, lakes and rivers. Swim only in protected swimming pools or safe sea water. Avoid drinking infected water. Wear protective footwear when walking in soil, especially if damp or water logged.

Natural History: Adult worms live for many years in mesenteric or vesicular veins. They release ova which cause granulomas and scarring of bladder and rectal mucosa. The ova are passed in urine and stool, hatch out into larvae in fresh water and then infect certain types of snail. The snails then release cercariae which can penetrate intact human skin during activities such as swimming, washing or paddling. After burrowing through the skin, the miracidia eventually migrate back to the intra-abdominal veins.

The illness: Initial infection is often asymptomatic but itching can occur at the site of entry. Two to four weeks later fever, diarrhoea, cough, rash and splenomegaly may develop.
S.haematobium later causes haematuria. Long-standing disease may cause ureteric obstruction and renal failure.
S.mansoni usually presents with anaemia due to blood loss and sometimes frank rectal bleeding. Complications in long- standing infection include diarrhoea, cirrhosis and portal hypertension.
S.japonicum causes an illness similar to S.Mansoni but is often more severe.

Treatment: Praziquantil can destroy adult worms but may not reverse all the mucosal damage if it is long-standing.

Recommended for more information
'Lecture Notes in Tropical medicine' . Dion R. Bell. Blackwell Publications ISBN 0-632-02445-0 or ' Mansons textbook of Tropical Diseases' Ed.G.C.Cook WB Saunders Company Ltd ISBN 0-7020-1764-7.