Climatic, environmental, and social factors in Visceral Leishmaniasis: A spatio-temporal perspective in Brazilian biomes

Vector-borne diseases (VBDs) remain a major global public health challenge, with considerable economic and social impacts. Phlebotomine sand flies, the vectors of the protozoan responsible for visceral leishmaniasis (VL), are highly sensitive to climatic and environmental conditions, which define biome characteristics. Brazil has six distinct biomes, offering a unique setting to explore the spatial variability of VL. We identified and compared climatic, environmental, and social variables associated with VL incidence (IncVL) across Brazilian municipalities and within each biome, excluding Pampa and Pantanal due to insufficient analytical robustness. The dependent variable was the triennial cumulative incidence of human VL (2008-2022). Independent variables included climatic factors (temperature mean and range, rainfall, and humidity), environmental factors (vegetation cover, land use, and urban density), and social indicators (illiteracy index, uncollected waste, and unconnected sewage system). To assess spatial dependence and the role of ecotone areas, we calculated univariate Global and Local Moran's I indices. Linear Mixed Models (LMMs) were then fitted for each biome and for Brazil overall, including municipality and time as random effects and accounting for spatial correlation (using R software). Nationally, IncVL was positively associated with mean temperature, savannah & grassland, and uncollected waste, and negatively associated with the illiteracy index. Each biome exhibited distinct relationships. In the Caatinga, IncVL was positively associated with forest formation, urban growth, and humidity range, and negatively with the illiteracy index and agriculture. In the Cerrado, it was negatively associated with agriculture and urban population. In the Amazon, it was positively associated with mean temperature and savannah & grassland, and negatively with mean humidity, deforestation, agriculture, and urban population density. In the Atlantic Forest, it was positively associated with mean temperature and savannah & grassland. These findings demonstrate that VL transmission patterns and their determining factors vary substantially across Brazilian biomes, underscoring the importance of region-specific surveillance and control strategies.