Rift Valley Fever Seroprevalence and Associated Risk Factors in Small Ruminants at Selected Human-Livestock-Wildlife Interfaces in Uganda

Background Following the first human Rift Valley fever outbreak after 48 years in 2016, Uganda has experienced sporadic outbreaks, especially in the cattle corridor since August 2017. Although wildlife potentially harbors RVFV strains, livestock exposure to RVFV at human-livestock-wildlife interfaces remains underexplored in major Ugandan conservation areas. Methods A cross-sectional quantitative study was conducted at Satellite Research Sites, located in Bwindi-Mgahinga, Lake Mburo, Queen Elizabeth, Murchison Falls, and Pian Upe conservation areas in Uganda, which were selected for their high human-livestock-wildlife interactions. Using a two-stage sampling design, small ruminants were sampled from randomly selected herds within villages adjacent to the national parks. Blood samples were collected, and analysed at the One Health Laboratory, via a validated in-house IgG indirect ELISA protocol. A structured questionnaire deployed in ArcGIS Survey123 captured the field data. Binary and logistic regression was performed on laboratory and field data. Results A total of 1,690 small ruminants were sampled: 92.4% (1555/1683) local breeds, 83.4% (1409/1690) goats, and 88.6% (1495/1687) females, with a mean age of 3 years. Overall RVFV seropositivity among small ruminants was 41.1% (695/1690), 95% CI (38.7–43.4%). The percentage of seropositive individuals per species was 42.4% (598/1409) in goats and 34.5% (97/281) in sheep. A total of 41.8% (625/1495) females, 42.4% (598/1409) of goats, and 55.5% (71/128) of exotic animals were more exposed to RVFV. Multivariable Poisson regression model analysis revealed that older animals (IRR = 1.10, 95% CI: 1.06–1.14, p < 0.001) were more seropositive, whereas local breeds (IRR = 0.77, 95% CI: 0.63–0.93, p = 0.009) presented reduced exposure to RVFV infection. Grazing from farms (IRR = 0.57, 95% CI: 0.39–0.81), dry-season park grazing (IRR = 0.69, 95% CI: 0.52–0.91), and watering animals from lakes (IRR = 0.75, 95% CI: 0.63–0.91), valley dams (IRR = 0.29, 95% CI: 0.14–0.63), or tanks (IRR = 0.53, 95% CI: 0.42–0.68) lowered the exposure risk to RVFV. Conclusion The high RVFV past exposure among small ruminants justifies the need for further studies to assess recent infections at the human-livestock-wildlife interface. Targeted interventions such as regulated park grazing, integrated vector control, and continuous surveillance should be implemented to minimize RVFV transmission in these high risk areas.