Prevalence and spatial distribution of trematode cercariae in vector snails within different agro-ecological zones in Western Kenya, 2016

Introduction: freshwater vector snails' distribution, infection with cercariae, preferred habitat and possible trematodiases transmission foci is not well known in Western Kenya. We sought to determine the distribution and prevalence of infection of snails per agro-ecological zone and environmental factors in vector snail habitats. Methods: we conducted a cross-sectional survey in March-May 2016, harvested and identified snails using shell morphology, determined their infection with trematode cercariae using microscopy, used descriptive statistics to estimate the prevalence of infection and relationship between snail abundance and environmental factors. Results: we sampled a total of 1,678 vector snails from 47 sampling sites of which 42% were Lymnaeid, 23% Biomphalaria, 10% Bulinus, 22% Oncomelaniae and 2% Melanoides. Lower Midland I Ago-Ecological Zones had 44% of the snails and streams from springs had 41% of the snails. Overall, 26.5% (445/1678) (95% CI: 24.4-28.6) of the snails shed cercariae. Cercariae were found in 11 (23%) of the sites and in all zones. F. gigantica cercariae were shed by L. natalensis, B. pfeifferi, B. sudanica. Lakeshore had both F. gigantica and S. mansoni cercariae shed by B. sudanica. A total of 72% (1,202/1,678) of snails were found in water with a pH 6.5-7.5. Grass habitat had 54% (912/1,678) of the snails. Conclusion: lymnaeid snails were present in all the zones, while streams from springs and near neutral habitats had most of the snails. Infection with trematode cercariae was noted in all the zones. Trematodiases control should be focused on all zones especially in freshwater streams and lakeshores.