Climate change and its impact on spatial and temporal distribution of visceral leishmaniasis transmission risk in Nepal

Visceral leishmaniasis (VL), also known as kala-azar, has posed significant challenges to elimination efforts due to increased reporting of new cases from high mountain and previously considered non-endemic areas in Nepal. Understanding the potential distribution of disease risk and its changing patterns in the context of climate change is vital to inform policies and target available resources effectively. In this study we modelled and mapped climatically (environmentally) areas suitable for VL transmission based on the ecological niche principle and machine learning modelling techniques. The results revealed that about 34% of the land area in the lowland Tarai region and river valleys in the hill and mountain regions of Nepal are currently suitable for VL transmission. Climate change is expected to increase the suitable area to 43% in the pessimistic scenario (SSP 585) for both time periods (2050s and 2070s), while the area at risk of transmission will remain static stagnant or slightly decrease in the optimistic scenario (SSP245) for both periods. Environmental suitability for VL transmission will decrease in the eastern lowland but increase in the West. The assessment of the proportion of the population at risk of VL transmission is about 81% which is expected to decrease in future, as VL risk decreases in some more densely populated areas. However, the predicted spatial shift of the population at risk will expose new populations at risk of transmission of VL. Our findings may contribute to design evidence-based health polices and to optimally target limited resources in the National VL Elimination programme.