The influence of environmental factors on the historical distribution of Biomphalaria pfeifferi in the Tshwane Metropolitan Municipality
Keywords: Schistosomiasis, Modelling, MaxEnt, S. mansoni, Biomphalaria pfeifferi (B. pfeifferi)
Abstract. Schistosomiasis remains the most endemic disease in tropical regions. Transmission rates and prevalence of schistosomiasis in Africa are relatively high compared to other regions. This is mostly associated with the lack of clean water and sanitation as necessities to curbing the spread of the disease. Over 90% of people in sub-Saharan Africa (SSA) are deprived of clean water and sanitation. 60-80% of the children in South African communities are infected. Climate variability plays a role in the distribution of vector-borne diseases by affecting intermediate host reproduction and changing their habitats thereby decreasing or increasing host survival and disease transmission ability. This study aims to determine the influence of environmental factors on the spatial distribution of Biomphalaria pfeifferi in the Tshwane Metropolitan Municipality. The use of species distribution models (SDMs) to model the intermediate snail hosts habitats in South Africa is uncommon, compared to other African countries. To our knowledge no modelling study has been done in South Africa particularly in the Tshwane Municipality, and this has therefore, paved a way for this study. A systematic literature review was conducted to identify all the important climatic variables that impact on the distribution of bilharzia-transmitting snails. Biomphalaria pfeifferi occurrence data was accessed from the National Freshwater Snails Collection, and the climate data was extracted from the ERA5 website respectively. The principal component analysis was used to reduce the multidimensionality of the dataset, with this framework tool, Pearson's correlations helped identify the variables showing a high correlation with the snail datasets and these were included in the ecological niche model. The following climatic variables: temperature, rainfall, water temperature, and other climate-related phenomena such as droughts and flooding influence the distribution patterns of intermediate snail hosts. The model showed high species presence along the central parts of Tshwane, mostly in the following areas Roodeplaat, Mamelodi, Winterveldt, and Refilwe. However, the south-eastern parts of the municipality did not indicate any species occurrence. The findings confirm that environmental factors impact on the historical distribution of Biomphalaria pfeifferi in the Tshwane Metropolitan Municipality. The response curves from the MaxEnt model depict the relationship between habitat suitability and environmental factors.