Comparative Studies of two Fresh Water Snail Distributions and Physico-Chemical Parameters in Selected Human Schistosomiasis Endemic Sites in Nigeria

Abstract

Combinations of abiotic and biotic factors exert their influences on fecundity, hence population density of snail hosts living in fresh water. However, only few distinct relationships have been established in snail ecology due to lack of precise data and difficulty in defining and evaluating the significance of an individual environmental factor. This investigation was carried out to evaluate combined effects of physico-chemical properties of fresh water on snail hosts population. The methods in Water Engineering and Development Centre (WEDC) Analytical methods Manual were used in water analysis. Fresh water bodies namely: Kanye and Rimin Gado Dams (Kano), Lagoon Front (Unilag, Akoka, Lagos) and Oyan Dam (Ogun-Osun River Basin, Abeokuta) were surveyed for three years. Two snail species namely Bulinus globosus (Morelet) and Bulinus rohlfsi (Clessin ) were specifically searched for and collected quarterly in these sites. Snail sampling for species of Bulinus globosus and Bulinus rohlfsi was carried out quarterly using standard technique involving drag scoop supplemented by a manual search. It was done duri ngdry and wet seasons. The contents of the scoop were searched by a visual inspection and by inspection of the underside of boats, bamboo rafts, floating and submerged sticks and vegetation. All snails collected from each station (i.e., scoop and manual searches) were pooled and recorded as number of snails per site per quarter. All snails were identified according to standard methods and mortalities recorded over a 3-year period were noted. The number of snails collected on each visit was correlated with prevailing physico-chemical parameters of sampled water bodies where these snails were collected. Test for infection was also carried out. Physico-chemical analysis of water from the selected sites showed that all the snails thrived better in oxygenated, slightly acidic (pH 5.6), low turbidity and low saline water. This might account for more snail populations recorded in Oyan Dam, Abeokuta and Kanye Dam in Kano. High prevalence of Schistosoma haematobium in these areas could therefore be explained.

Keywords: Physico-chemical, Snails, B. globosus, B.rohlfsi, Freshwater

Nigerian Journal of Parasitology, Vol. 32 [2] September 2011, pp.169-174