Inter-epidemic seroprevalence of Rift Valley fever virus and associated risk factors in humans in Eastern Rwanda

Rift Valley fever (RVF) is a mosquito-borne zoonosis that causes periodic and explosive epizootics/epidemics in Africa and the Arabian Peninsula. In Rwanda, RVF virus (RVFV) circulation has resulted into two major outbreaks in 2018 and 2022, both of which involving humans. Information on the magnitude of human exposure to RVFV in the country is scarce. This cross-sectional study aimed to investigate the seroprevalence of RVFV and associated risk factors in humans in the Eastern province of Rwanda, 3 years after the end of the 2018 outbreak.

A total of 552 outpatients at health facilities in five districts of the Eastern province were randomly sampled and interviewed between December 2021 and February 2022. Exposure to RVFV was examined by detection of anti-RVFV IgG/IgM antibodies in serum samples using a competitive enzyme linked immunosorbent assay (c-ELISA). Bivariate and multivariate logistic regressions were used to assess the association between risk factors and RVFV seropositivity.

The findings revealed an overall seroprevalence of 9.6%. The highest seropositivity, but without significant difference, was observed in Bugesera district (12.9%), followed by Kayonza, (10.8%), Kirehe (8.6%), Rwamagana (7.0%) and Ngoma (6.8%). Odds of seropositivity were significantly higher in people with a history of slaughtering animals (OR 2.26, 95% CI 1.04 - 4.91, p = 0.03), and milking (OR 2.60, 95% CI 1.23 - 5.49, p = 0.012). Sex and age-related differences were not significant.

This study is a first serological survey of RVFV spillover to humans in the country and shows that rural communities in Rwanda have been exposed to RVFV. These findings suggest the Eastern province of Rwanda as a potential hotspot for RVFV circulation, and emphasize the need for a countrywide One Health-based surveillance, prevention, and control strategy to minimize the effects of RVFV in the country.