Prevalence of Snail Vectors of Schistosomiasis in the Kpong Head Pond, Ghana

Abstract

Schistosomiasis, a parasitic disease caused by the blood fluke Schistosoma sp. became a serious public health problem in Ghana after the Volta River was dammed in Akosombo in 1964. The formation of the Kpong head pond, about 25 km below the Akosombo dam, as a result of a second dam built at Kpong became an active schistosomiasis transmission site. The Volta River Authority (VRA) recently began an initiative of combining manual clearing of aquatic vegetation with chemotherapy as a way of managing the disease. However, no scientific monitoring of the effect of aquatic weed clearing on the vector population is being conducted. The study was initiated in the Kpong head pond to provide baseline data for subsequent monitoring and impact assessment of the initiative. It involved sampling of the banks of the head pond for aquatic snails at six different sampling sites of 1 m2 each, chosen at 100 m interval along the shoreline. Physicochemical factors which affect aquatic snail population were also determined. Aquatic snails sampled were Bulinus truncatus, Bulinus globosus, Biomphalaria pfeifferi, Melanoides spp, Physa waterlotti and Pila sp. where the first three are intermediate host of the schistosoma parasite. The study revealed B. truncates as the most frequent occurring vector (71.0%), followed by Biomphalaria (12.0%) and B. globosus (6.1%) The mean numbers of vector snails sampled per m2 were B. Truncates 61/m2, B. globosus 5/m2, and B. pfeifferi 11/m2. The presence of aquatic weeds and favourable physicochemical conditions of the water were found to provide a conducive environment for the vectors to thrive and hence sustain schistosomiasis transmission in the head pond. It is, therefore, recommended that a 5-year period of studies be undertaken to assess the impact of manual clearing of aquatic weeds on the snail population.