Ecological studies of Bulinus rohlfsi, the intermediate host of Schistosoma haematobium in the Volta Lake

Abstract

In the present ecological study of cercarial transmission of Schistosoma haematobium in the Volta Lake, Ghana, habitat observations and sampling of Bulinus truncatus rohlfsi were conducted within a 60-km stretch of shoreline. Observations revealed that human water contact sites in each village undergo constant changes in shape and vegetation. Snail sampling surveys in water contact sites were carried out monthly (for 27 months) in 8 villages using newly designed palm-leaf traps, and in 8 additional villages (for 16 months) using a modification of Olivier & Sneidermann's man-time method. Results to date confirm the finding by Chu & Vanderburg that cercarial transmission in the lake takes place almost exclusively within water contact sites. Additional results indicate that even within individual water contact sites this transmission is focal, most infected snails being found very close to the shoreline. Transmission also varies significantly according to shape, vegetation, and geographical location of the water contact sites, and is distinctly seasonal in most villages. These findings lead us to conclude that control of cercarial transmission in the Volta Lake is both attainable and feasible with existing methods.