Background

Schistosomiasis (often known as bilharzia) is a tropical disease of considerable public health and socio-economic importance in the developing world, and is the second most prevalent tropical disease in sub-Saharan Africa after malaria (Kabatereine et al., 2004). In Uganda it is estimated that four million people are infected with schistosomiasis especially in areas of high risk to the disease. For instance schistosomiasis is endemic in the West Nile region and studies have reported the prevalence in certain areas to be over 80%.

The disease is wide-spread among poor populations living in conditions that favour transmission, for instance fishing communities living along shores of lakes and rivers, and those that do not have access to clean and safe water sources that are free from contamination with faecal material.

With its many lakes, rivers, streams, swamps and ponds Uganda has a diverse fresh water environment that offers numerous and suitable habitats for the Biomphalaria species of aquatic snails that carry the parasite Schistosoma mansoni (Kazibwe et al., 2006). Cercariae, the infective larval stages of the parasite, are released by snails into the water and these are able to swim and penetrate human skin.

Although many people are infected, the disease receives less attention than it merits (Van Der Werf et al., 2003). This is partly because not everyone who is infected shows clinical signs. The degree of pathology depends on the worm burden and the host's immune response to the eggs, while the degree of morbidity associated with the disease is related to the intensity of infection. Schistosomiasis rarely results in death, but it is nevertheless a severely debilitating disease.

Most studies on schistosomiasis appear to have primarily focused on determining the prevalence and control of the disease in humans and less on relating disease levels with snail incidence. It was therefore decided to conduct an epidemiological study to assess both the incidence of the disease in aquatic snails that transmit the parasite and its prevalence in adjacent human communities living close to water.