Understanding the Rift Valley fever exposure risk: A comparative perspective from a multi-country study in East and Central Africa, 2021-24

Rift Valley fever (RVF) is a concern in East and Central Africa, particularly following periods of heavy rainfall and flooding. However no human outbreaks have been reported in the Democratic Republic of the Congo (DRC). To assess whether this reflects a true absence of virus circulation, we estimated RVF seroprevalence in Goma (eastern DRC) and examined context-specific risk factors, comparing the findings with data from outbreak-prone countries. A two-year longitudinal study, across six health facilities in DRC, Kenya and Uganda, enrolled febrile subjects aged ≥10 years. Human serum samples were analyzed for RVF virus and anti-RVF antibodies. Demographic, behavioral, occupational and environmental factors were evaluated. 4,806 participants were enrolled: 1,370 (28.5%) DRC, 1,468 (30.6%) Kenya and 1,968 (40.9%) Uganda. 253 participants (5.3%) tested positive for RVF by serological and/or molecular assays: 19 (1.4%) DRC, 29 (2.0%) Kenya and 205 (10.4%) Uganda (p < 0.001). Only in Uganda, subjects tested positive for RVF virus by PCR (10 subjects, 0.5%). Occupations and activities involving contact with livestock, predominated in Kenya and Uganda, whereas handling of raw meat was most common in DRC. No specific occupations or activities were significantly associated with RVF exposure in DRC while several significant factors were identified for Kenya and Uganda. Multivariate analysis across all three countries showed that being from Uganda, male, over 20 years of age, employed as butcher or crop farmer and engaging in animal-related activities, were independently associated with RVF positivity, as was contact with sheep. Despite a prevailing sense that RVF transmission does not occur in DRC, we found a seroprevalence of 1.4%, comparable to Kenya where RVF is well documented. Further research targeting high-risk human and animal populations in DRC is warranted. A One Health approach will contribute to defining the ecology of local transmission of RVF in DRC.