Spatial modeling of risk factors for human exposure to West Nile virus in rural Madagascar
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Background West Nile virus (WNV) is an emerging disease transmitted from bird hosts to humans by Culex mosquitoes. Thousands of human cases of WNV infection are reported each year in the United States and Europe, and circulation has been confirmed in Africa and the Indian Ocean, including Madagascar. However, little is known about the current riskscape for people in Madagascar, and what determines its local distribution and human exposure across the population. The goal of this study was to assess WNV seroprevalence and identify associated socio-ecological risk factors in rural Madagascar. Methodology and principal findings A cross-sectional serological survey was conducted in Ifanadiana District in 2021, nested within a representative longitudinal cohort. We evaluated serological responses to WNV and to Dengue virus in 3,948 individuals using a multiplex bead assay. We estimated WNV seroprevalence using a Gaussian Mixture Model (GMM) and characterized environmental, socioeconomic, and demographic factors that could be associated with exposure to WNV using various data sources, including optical and Synthetic Aperture Radar (SAR) satellite images, climate variables, and household survey data. Overall seroprevalence was 43%, and populations living in geographically isolated areas and those engaged in agricultural activities were at higher risk, while proximity to dense forests and residential areas were protective against WNV exposure. Conclusions This study found high rates and local heterogeneity in WNV exposure in a rural district of Madagascar. In addition, environmental, climatic, and socio-demographic data were determinants of WNV transmission, providing a valuable tool for surveillance and decision-making in arbovirus prevention and control. Extending this approach to other orthoflaviviruses could improve understanding of local viral co-circulation and promote the development of more precise and context-specific prevention strategies.
