Modeling the current spatial distribution of snail intermediate hosts of schistosomiasis using Maxent software in the Volta Basin (Burkina Faso)

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Résumé

Background The socioeconomic consequences of schistosomiasis have forced the integration of control strategies. Currently, all control efforts have tended to involve the control of snail intermediate hosts. However, the integration of snail control into the general schistosomiasis control strategy has not yet been effective in Burkina Faso. While snail occurrence data have been collected intermittently since the last systematic assessment in 1980, there has been no recent synthesis of the distribution of intermediate host snails in Burkina Faso. The aim of this study was to integrate historical and recent datasets to assess temporal shifts in species distribution, identify key climatic drivers, and produce spatially explicit risk maps to support targeted control strategies in Burkina Faso. Methods Snail occurrence data were compiled for three time periods: 1980, 2018, and 2021. Data from 1980 and 2018 were obtained through a comprehensive literature review, while field sampling was conducted in 2021 in two basins: the Mouhoun basin and the Nakanbé basin. The Maximum Entropy (Maxent) modeling approach was used to predict changes in species distributions over time by integrating occurrence records from each period with relevant environmental variables. Model performance was evaluated using the Area Under the Curve (AUC) of the Receiver Operating Characteristic (ROC) curve and the Boyce index. The contribution of each environmental variable was assessed using a jackknife test. Results Five schistosomiasis intermediate hosts were collected: Bulinus truncatus, Bulinus forskalii, Bulinus senegalensis, Bulinus globosus, and Biomphalaria pfeifferi . The number of snail intermediate host species for schistosomes did not significantly change between 1980 and 2021. Except for B. umbilicatus , the results show that the two basins host almost the same species of snail intermediate host of schistosomes. The rivers, reservoirs, and irrigated plains provide favorable conditions for the occurrence of all species of snail intermediate hosts. The area under the curve (AUC) of the selected variables ranged from 0.877 to 0.985. Except for B. globosus , the Boyce index ranged from 0.6 to 0.924. Spatial distribution modeling indicated that the western part of the Volta Basin is more suitable for the occurrence of schistosome intermediate host snails. Conclusions Schistosomiasis intermediate host snails are common in the Nakanbé and Mouhoun basins, where suitable habitats are widespread. The Maxent model successfully identified areas with high environmental suitability for these intermediate host snails. This study integrated historical and recent occurrence data to assess temporal changes in intermediate host snail distribution, identify key climatic drivers of distribution shifts over the past 40 years, and highlight priority areas for targeted snail control in Burkina Faso.

Mots-clés

Snail, Schistosomiasis, Spatial distribution, Current (fluid), Structural basin, Software, Distribution (mathematics)