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. Author summary: Leishmaniasis is a common disease in tropical and subtropical regions, but it also occurs in southern Europe. While some infectious disease experts are concerned that climate change might lead to the emergence of new diseases in new areas, the main factors shaping leishmaniasis in Europe are not well understood. This study considered a wide array of potential risk factors in a variety of categories, ranging from climate and nature to how people live and work. We found that the risk for leishmaniasis is mostly related to occupation, housing type, age, and sex, though the exact risk factors change from country to country. People with weakened immune systems face high risk, and infected animals pose a major threats, but climate change alone may not drive the spread of leishmaniasis as much as once feared. Interestingly, a healthy variety of wildlife may help keeping the disease in check. To limit the impacts of leishmaniasis, we need to protect the most vulnerable populations, such as people living with weakened immune systems, working in high-risk sectors, residing in single-dwelling buildings, or experiencing or facing homelessness. We need to monitor the parasite in people and animals and share those surveillance data openly. Ultimately, we need a “One Health” approach where doctors, social workers, and scientists work together to keep our ecosystems healthy and our communities safe.