STUDIES ON THE EFFECT OF CERTAIN MOLLUSCICIDAL AGENTS ON THE SNAIL INTERMEDIATE HOST OF SCHISTOSOMA MANSON

Abstract

Schistosomiasis is a disease transmitted by some fresh water snails, most notably of the genera Biomphalaria , Bulinus and Oncomelania . The disease is endemic in the tropical and subtropical areas of the world, and affects more than 300 million people, and a further 600 million people are probably at risk (Mott, 1989). At present, various methods including health education, mass chemotherapy, and snail control have been recommended to control this disease or reduce the risk of re-infection.

Destroying the snails which harbour the developing schistosoma larvae is one way to interrupt the parasite's life cycle and prevent human infection. However, snail control operations including synthetic and plant mollusciciding will remain among the methods of choice for the control of schistosomiasis.

Considerable success has been achieved by the use of synthetic molluscicides for the elimination of snails which transmit cercariae. Such molluscicides include copper sulphate, trienrnorph, Bayluscide and sodium pentachlorophenate (Marston and Hostettman , 1985) . Economically, these synthetic molluscicides are expensive and in addition, may lead to problems of toxicity to non-target organisms and deleterious long-term effects in the environment. The use of plants with molluscicidal properties is an inexpensive, simple and appropriate technology for focal control of the snail vector (Hostettmann, 1984 ).