Socioeconomic risk factors and human immunosuppressive conditions are major drivers of human leishmaniasis in southern Europe

Background Leishmaniasis is endemic in southern Europe with high risks of outbreaks and geographical spread. However, the risk factors for human leishmaniasis are understudied in this region. Methodology To evaluate these risk factors, we tested associations between leishmaniasis incidence and an array of variables related to socioeconomics, immunocompetence, climate, land use, biodiversity, and ecology (i.e., the pathogen and its vectors and reservoirs). Findings Socioeconomic factors, such as demography, occupation, and housing conditions, were strongly associated with leishmaniasis incidence in endemic regions. The specific factors and the magnitude of their impacts varied among the five countries studied. Human immunosuppressive condition was highly correlated with leishmaniasis risk in Spain and Italy. Climate likely delineated leishmaniasis-free regions from endemic regions in France. Our results suggest that climate change alone may not drive the spread of leishmaniasis within this century. Pathogen hazard and reservoir abundance affected leishmaniasis risk more than vector hazard in countries where data were available. Biodiversity was weakly, negatively related to leishmaniasis. Significance Our results highlight the importance of socioeconomic risk factors and immunosuppression for human leishmaniasis, suggesting potential implications for disease control and prevention policies. Surveillance of Leishmania spp. in humans, vectors, and reservoirs; assessment of reservoir abundance; and data accessibility are crucial for disease prevention and preparedness. Because of possible biodiversity regulation, efforts to understand and control leishmaniasis could benefit from a One Health approach that involves epidemiologists, social scientists, and ecologists, among others.