Predicting current habitat suitability for intermediate snail hosts of urogenital and intestinal schistosomiasis in the Lower Shire Valley floodplain of southern Malawi

This paper presents the first species distribution models (SDMs) for intermediate snail hosts for urogenital and intestinal schistosomiasis in Chikwawa and Nsanje Districts, which together form the Lower Shire Valley (LSV) in Malawi. The SDMs developed for this study are ensemble machine learning approaches based on Random Forest (RF), Support Vector Machines (SVM), and multilayer perceptron (MLP) and are specific to the Bulinus africanus group and Biomphalaria pfeifferi. The former transmits urogenital schistosomiasis (Schistosoma haematobium), while the latter transmits intestinal schistosomiasis (Schistosoma mansoni), both of which affect nearly 240 million people globally. This study addresses the following questions: 1. Where are the most suitable habitats for intermediate host snails in the LSV? 2. Which environmental factors are strongly associated with the geographical distribution of such snails in the LSV? Consistent with expectations, the SDMs reveal the following: 1) currently, Bu. africanus group not only has a wide distribution across central Chikwawa and eastern Nsanje but is also concentrated in floodplains, and the LSV has few habitats that can support Bi. pfeifferi, 2) vegetation cover is the most important predictor of Bu. africanus group distribution, whereas precipitation variables are most important for Bi. pfeifferi in the LSV. Understanding the spatial and temporal distributions of these snails is important for controlling and eliminating schistosomiasis.