Visceral Leishmaniasis Prevalence Forecast for 2040: A Global Overview of 99 Endemic Regions and Countries Using Illness-Death Modeling

Background: Visceral leishmaniasis (VL) is a fatal parasitic disease endemic to tropical regions and associated with severe complications and high mortality. Persistent challenges such as delayed diagnosis and limited treatment options highlight the urgent need for robust predictive epidemiological models. Study Design: This study was a secondary analysis conducted using cross-sectional data. Methods: Sex-specific VL epidemiological data from 1990 to 2021 were obtained from the Global Burden of Disease (GBD) database and analyzed globally and across 98 endemic countries and regions. An enhanced illness-death model (IDM), incorporating remission, was applied to estimate the age-standardized prevalence rate (ASPR) of VL by 2040. Results: Globally, the global ASPR of VL decreased by 94.68% between 1990 and 2021. It is projected to decrease by an additional 72.55% by 2040, declining from 0.108 in 2021 to 0.030 (95% CI: 0.020, 0.043) per 100,000 population. In 2040, ASPR is expected to remain higher in males than in females (0.041 vs. 0.019). Tropical Latin America is projected to have the highest regional ASPR at 0.583 (95% CI: 0.565, 0.602). Western Sub-Saharan Africa is the only region expected to experience an increase, rising by 417.12%. Of 83 nations, 27 are expected to exhibit increasing trends, with Djibouti demonstrating the highest projected ASPR at 20.32 (95% CI: 5.25, 78.67), a 2050.59% increase from 2021 to 2040. Conclusion: Despite global declines in VL prevalence, significant increases are expected in Western Sub-Saharan Africa and countries such as Djibouti, highlighting the need for targeted interventions. Strengthening healthcare systems, improving vector control, and addressing sex-specific risks are crucial to maintain global progress.