Influence of water physico-chemical properties and vegetation type on the distribution of schistosomiasis intermediate host snails in Nelson Mandela Bay, South Africa

Abstract

Schistosomiasis is an infectious water-borne disease transmitted by Schistosoma flatworms. Humans become infected through skin penetration following exposure to water contaminated with schistosome cercariae. This study assessed the physico-chemical properties of the water bodies, vegetation type, distribution and habitat presence of the snail intermediate hosts. A quantitative cross-sectional research design was used to collect samples in eight waterbodies near residential areas over a nine-month period in 2023. Physico-chemical properties were measured using hand-held meters. A mesh scoop net was used to capture snails. Vegetation cover was visually estimated and recorded at each sampling point. Data was analysed using R software (version 4.3.1). A total of 844 freshwater snails were collected, including Bulinus (0.9%) and Biomphalaria (0.6%) which are the only genera serving as intermediate hosts for schistosomiasis in South Africa. Indicator macrophytes and floating macroalgae were found in several water bodies. A negative and weak correlation existed between snails and physico-chemical properties such as: EC (r = −0.240), DO (r = −0.185), hardness (r = −0.210), pH (r = −0.235), salinity (r = −0.242), temperature (r = −0.273), and TDS (r = −0.236). Moreover, a negative and weak correlation existed between snails and vegetation coverage (r = −0.127). Snail abundance marginally declined with rising physico-chemical concentrations, and the majority of snails were found in regions with less vegetation cover.