Seroprevalence of rift valley fever virus and associated risk factors in small ruminants at human-livestock-wildlife interface within Uganda’s conservation areas

TL;DR

This study found a high rate of past exposure to Rift Valley Fever Virus in small ruminants at the human-livestock-wildlife interface in Uganda's conservation areas.

Contribution

The study provides new insights into RVFV seroprevalence and risk factors among small ruminants in conservation areas with high human-livestock-wildlife interactions.

Findings

Overall RVFV seropositivity in small ruminants was 41.1%, with higher rates in goats (42.4%) compared to sheep (34.5%).

Exotic breeds and females had higher seroprevalence rates at 55.5% and 41.8%, respectively.

Older animals had increased risk of RVFV exposure, while local breeds had reduced exposure risk.

Abstract

Following the first laboratory confirmed human Rift Valley Fever Virus (RVFV) outbreak in 48 years, Uganda has continued to detect sporadic outbreaks, particularly within the cattle corridor since 2016. Although wildlife potentially harbors RVFV strains, livestock exposure to RVFV at human-livestock-wildlife interfaces remains underexplored in major Ugandan conservation areas.

A cross-sectional quantitative study was conducted between August, 2022 and March, 2023, at Satellite Research Sites (SRS), 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 with a validated in-house IgG indirect ELISA at the One Health Laboratory. ArcGIS Survey123 was used to capture the field data. Modified Poisson regression for binary outcomes and relative risks estimates were used.

A total of 1,690 small ruminants were sampled: 83.4% goats (caprine species), 16.6% sheep (ovine species). Of these, 92.4% were local breeds and 7.6% were exotic breeds. The females were 88.6% and 11.4% were males, with a mean age of 3 years. Overall RVFV seropositivity for both sheep and goats was 41.1% (695/1690), 95% CI (38.7–43.4%). Seropositivity per species was 42.4% (598/1409) in goats and 34.5% (97/281) in sheep. Exotic breeds and females had higher RVFV seroprevalence rates at 55.5% (71/128) and 41.8% (625/1,495) respectively. Modified Poisson regression analysis revealed that older animals (RR = 1.10, 95% CI: 1.06–1.14, p < 0.001) had higher risk of RVFV seropositivity, whereas local breeds (RR = 0.77, 95% CI: 0.63–0.93, p = 0.009) had reduced exposure risk to RVFV. Low RVFV exposure was evidenced in different management systems of grazing and watering the small ruminants.

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.

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