Freshwater Vector Snails and their Infection with Trematode cercariae in Busia County

Capturing snails

In this study, we  sought to identify snail species infected with Trematode cercariae and environmental factors that correlate with their presence.  This was undertaken to better understand the underlying biology of these species to better understand the risk of transmission of livestock- and human-infectious trematodes.

We found that lymnaeid snails were widely distributed in all the agro-ecological zones (AEZs) we studied, and were the majority snail

at low altitudes. Biomphalariae, Bulinus, Oncomelaniae and Melanoides were present in some but not all of the zones. The study found that snails were more abundant in streams originating from springs and swamps near the shores of Lake Victoria. Biomphalariae and Lymnaeid species were found to be infected with trematode cercariae. The B. sudanica species found in the swamps near the lakeshore were infected with both Fasciola gigantica and Schistosoma mansoni pointing to a co-existence of Schistosoma and Fasciola infection at the site. The relative abundance of vector snails was found to be influenced by water pH, water temperature, ambient temperature and vegetation cover.

Identification/Isolation of cercariae

The presence of vector snails and cercariae in all of the zones points to the presence of possible transmission foci for Schistosomiasis, Fascioliasis and other foodborne trematodiases. People and animals using water and pasture from these sites in western Kenya are at a risk of contracting these parasitic infections.

Control of foodborne trematode infection should be targeted in all the AEZ’s with emphasis placed on the areas that border the lake and those with streams flowing from springs.

Article by Maurice Omondi Owiny, Resident, Kenya FELTP. Resident, Kenya Field Epidemiology and Laboratory Training Programme based at the International Livestock Research Institute