Molluscicide Health Dictionary

Also known as BILHARZIASIS. This infection results from one of the human Schistosoma species. It is common in Africa, South America, the Far East, Middle East, and, to a limited extent, the Caribbean. The life-cycle is dependent on fresh-water snails which act as the intermediate host for the ?uke; the cercarial stage of the ?uke enters via intact human skin and matures in the portal circulation. Clinically, ‘swimmers’ itch’ may occur at the site of cercarial skin penetration. Acute schistosomiasis (Katayama fever) can result in fever, an urticarial rash (see URTICARIA), and enlargement of LIVER and SPLEEN. The adult male is about 12 mm and the female 24 mm in length.

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; diarrhoea, which may be bloody, can be a presenting feature. In a heavy infection, eggs surrounded by granulomas are deposited in the liver, giving rise to extensive damage (pipe-stem ?brosis) associated with PORTAL HYPERTENSION, oesophageal varices, etc. However, unlike in CIRRHOSIS, hepatocellular function is preserved until late in the disease. S. japonicum (which is con?ned to the Far East, especially Indonesia) behaves similarly to S. mansoni infection; liver involvement is often more severe.

Diagnosis can be made by microscopic examination of URINE or FAECES. The characteristic eggs are usually detectable. Alternatively, rectal or liver BIOPSY are of value. Serological tests, including an ELISA (see ENZYME-LINKED IMMUNOSORBENT ASSAY (ELISA)), have now largely replaced invasive procedures used in making a parasitological diagnosis.

Treatment CHEMOTHERAPY has been revolutionised by the introduction of praziquantel (administered orally); this compound has no serious side-effects, although its cost may limit its use in developing countries. Oxamniquine is cheaper and e?ective in S. mansoni infection, although evidence of resistance has been recorded in several countries. Metriphonate is also relatively cheap and is of value in S. haematobium infection. Prevention is by complete avoidance of exposure to contaminated water; all travellers to infected areas should know about this disease. It is increasing in frequency as new expanses of fresh water appear as a result of irrigation schemes and dam projects. Molluscicides can be employed for snail-control.... schistosomiasis