Seroprevalence of Arbovirus-specific Antibodies in Blood Donors in the Republic of the Congo

Background: Evidence on previous exposure to arboviruses in the Republic of the Congo is geographically limited. Serological testing of archived donor specimens can describe historical antibody patterns, although results depend on the assays used. Objective: To describe IgG reactivity to eight arboviral targets among blood donors sampled at six locations in the Republic of the Congo in 2011. Methods: In a cross-sectional survey conducted from March to June 2011, sera from 1,009 eligible donors aged 18–65 years were examined by IgG ELISA for seven arboviruses and indirect immunofluorescence for Crimean–Congo hemorrhagic fever virus (CCHFV). ELISA-positive or borderline results for yellow fever virus (YFV), West Nile virus (WNV), Toscana virus (TOSV) and tick-borne encephalitis virus (TBEV) underwent virus neutralization testing (VNT). Frequencies, proportions and Wilson 95% confidence intervals were summarized descriptively. Results: Of 1,009 donors, 934 (92.6%) were recruited in urban sites and 754 (74.7%) were male. ELISA IgG reactivity was recorded for dengue virus (DENV) in 456 donors (45.2%), chikungunya virus (CHIKV) in 367 (36.4%) and Rift Valley fever virus (RVFV) in 77 (7.6%). VNT-positive results were observed for YFV in 281 (27.8%), WNV in 246 (24.4%), TOSV in six (0.6%) and TBEV in one (0.1%). No CCHFV IgG reactivity was recorded by immunofluorescence. These assay-defined proportions are not directly interchangeable across viruses. Conclusion: Antibodies reactive with several arboviral targets were detected in this historical donor sample. The findings support geographically broader, contemporary studies using comparable confirmatory assays and vaccination histories, but do not establish recent infections or current transmission intensity.