Spatial and temporal analysis of Rift Valley fever outbreaks in livestock in Uganda: a retrospective study from 2013 to 2022.

Background: Rift Valley fever (RVF) is a zoonotic disease caused by the Rift Valley fever virus (RVFV), primarily affecting livestock and transmitted by Aedes mosquitoes. First detected in Kenya in 1930, RVF has since spread across Africa, including Uganda, and to the Arabian Peninsula. Uganda reported its first human cases of RVF in 1968, with sporadic outbreaks continuing since the significant outbreak in 2016, particularly in regions with high livestock populations. Although RVFV was detected in mosquitoes in Uganda as early as 1944, the spatial and temporal distribution of RVF outbreaks has not been thoroughly documented. This study aimed to analyze trends in RVF outbreaks across Uganda from 2013 to 2022 to provide insights for effective control measures. A retrospective study was conducted utilizing archived RVF data from NADDEC, along with rainfall and temperature data from the Uganda Meteorological Centre. Maps were generated using QGIS software to illustrate the spatial distribution of RVF outbreaks. The distribution and trends were analyzed using the R programming language.

Results: During the study period, RVF outbreaks were reported in 74.1% of districts surveyed, representing 27.2% of all districts nationwide. The overall RVF seropositivity among tested animals was found to be 13.02% [95% CI: 12.4-13.7%], with bovine exhibiting the highest RVF seropositivity among the commonly raised species, such as cattle, goats and sheep. The year 2017 recorded the highest RVF seropositivity at 19.6%. Notably, the central region had the highest RVF seropositivity at 17.7% [95% CI: 15.8-19.7%] while the eastern region recorded the lowest at 4.6%.

Conclusion: This analysis provides crucial insights into the spatial and temporal patterns of RVF outbreaks in Uganda, emphasizing the need for targeted interventions, strengthened surveillance, and interdisciplinary collaboration. Despite significant number of studies on RVF outbreaks and prevalence over recent years, little is known about the virus's maintenance mechanisms in the absence of visible outbreaks. Potential reservoirs, vector dynamics, and environmental factors that facilitate its survival and re-emergence remain poorly characterized. Addressing these gaps is critical to improving early warning systems, guiding targeted surveillance, and implementing effective control measures to mitigate future outbreaks.