Determination of infection rates of snail populations is one of the basic tools for studies on the epidemiology of snail borne diseases.  In this study, we opted to determine the trematode infection of freshwater snails found in the OMO-Gibe river basin, Southwest Ethiopia. This study is based on a dataset of 130 samples collected from lakes, wetlands, rivers, dam reservoir shores and irrigation canals.  The snails were examined for trematode infections by cercarial emergence immediately after collection. Habitat conditions, water quality and human water contact practices and other human activities were assessed at each observation site.  A total of 3045, snails belonging to five species, were collected. The most abundant species was Biomphalaria pfeifferi, representing 66 % of the total collection. Overall, 109 (3.6%) of the snails were found to infected with trematodes (cercariae). Biomphalaria pfeifferi was found to be the most heavily infected, accounting 85% of the total trematode infection. A total of eight morphologically different types of cercariae were recovered. The type of cercariae recorded were Echinostome, BAD (Brivifurcate Affaringeate Diastome), Amphistome cercariae, BAM (Brivifurcate Affaringeate Monostome), Xiphidiocercaria, Longifurcate Pharyngeate Distome (LPD), Strigea cercariae and unidentified cercariae. BAD (Brivifurcate affaringeate diastome) and Echinostome cercariae were the most abundant cercariae, accounting 36.8% and 34% of the total infection respectively. Overall, the abundance, occurrence and infection rate of snail species were largely influenced by water physicochemical quality, sanitation and water contact behaviour of the inhabitants. Human activities such as open field defecation, urination, livestock grazing, farming, and swimming were important predictors for the abundance of cercariae. Therefore, proper containment of excreta (urine and faeces), reducing human and animal contacts to surface water should halt trematode infection and reduce snail borne diseases transmission.

Key words

Biomphalaria pfeifferi; Cercariae, Freshwater, Schistosomiasis, Snail, Trematode