Abstract
Schistosomiasis is an economically important disease of man and livestock caused by trematode parasites of the genus Schistosoma. The disease is wide-spread and endemic throughout many parts of the world infested by the intermediate freshwater snail hosts belonging to the family Planorbidae. The affected areas include; Africa, Madagascar, S. America, India, Sri Lanka, South East Asia, China, Japan, Philipines, Taiwan, Indonesia and the Caribbean (Rollinson and Southgate, 1987), 75 countries in all. It is estimated that 250 million people are infected with schistosomes whilst another 600 million people are exposed to the risk of infection. In endemic rural areas of many developing countries, schistosomiasis is an important occupational hazard (Doumenge, Mott, Cheng, Villenave, Chapuis, Perrin and Reaud-Thomas, 1987). Earliar reports indicated that, in Ghana, schistosomiasis was focal, occurring only in certain localized areas until the creation of the Volta dam in 1964 (Odei, 1964; Derban, 1983; Okoh, 1994). Today, schistosomiasis is known to occur in all regions of Ghana, especially among the riparian communities, some of which have registered prevalence rates as high as 100% for urinary schistosomiasis (Okoh, 1994). The creation of the Volta dams at Akosombo and Kpong, and the construction of dams and reservoires in various other parts of the country, have provided very siutable breeding sites for the Planorbid snail intermediate hosts, resulting in changes in the transmission patterns of the disease. The risk of transmission of bilharziasis continues to be aggravated as fishermen attracted by the Volta lake move from place to place while fishing and thereby contribute to the spread of the disease to previously uncontaminated areas. Both Odei (1975) and Okoh (1994) emphasized that this situation has made several water bodies in Ghana public health liabilities, thus undermining their economic importance.
