Influences of Rainfall and Temperature Trends on the Transmission and Control of Visceral Leishmaniasis (VL)

Visceral Leishmaniasis (VL), transmitted by more than 90 sandfly species, remains a major global health concern. Climate variables such as temperature and rainfall strongly affect sandfly life cycles and VL transmission, yet most models assume constant biological responses. Incorporating climate variability can enhance predictive accuracy and inform effective control strategies. We propose an SEIR-type model for VL transmission that integrates seasonal variations in rainfall and temperature through periodic sandfly recruitment, biting, and mortality rates. The non-autonomous differential equations model is calibrated with meteorological and epidemiological data from Ethiopia, a VL endemic region. A time-averaged basic reproduction ratio is derived for the system. The calibrated model with observed climate trends shows that the reproduction ratio peaks at moderate weekly temperatures with low rainfall, and declines during extreme rainfall and temperature periods. A temperature decline of 0.417 per decade creates conditions favorable to sandflies, potentially intensifying transmission, while a rainfall increase of 0.062 per decade reduces infections by 30.13% over 278 intervention weeks. Implementing a maximum of 50% effective vector control effort reduces cases by 66.70% under current climate trends. These findings underscore the crucial role of temperature and rainfall variability in shaping VL dynamics and the value of climate-sensitive interventions. They further emphasize the importance of evaluating future VL control strategies under IPCC climate scenarios to guide adaptation and mitigation efforts.