High Seroreactivities to Orthoebolaviruses in Rural Cameroon: A Case-Control Study on Nonhuman Primate Bites and a Cross-sectional Survey in Rural Populations

Abstract

Background: Ebola (EBOV) and Sudan (SUDV) orthoebolaviruses are responsible for lethal hemorrhagic fever outbreaks in humans in Central and West Africa, and in apes that can be at the source of human outbreaks for EBOV.

Methods: To assess the risk of exposure to orthoebolaviruses through contact with nonhuman primates (NHP), we tested the presence of antibodies against different viral proteins with a microsphere-based multiplex immunoassay in a case-control study on bites from NHPs in forest areas from Cameroon (n = 795) and in cross-sectional surveys from other rural populations (n = 622) of the same country.

Results: Seroreactivities against at least 2 viral proteins were detected in 13% and 12% of the samples for EBOV and SUDV, respectively. Probability of seroreactivity was not associated with history of NHP bites, but was 3 times higher in Pygmies compared to Bantus. Although no neutralizing antibodies to EBOV and SUDV were detected in a selected series of highly reactive samples, avidity results indicate strong affinity to SUDV antigens.

Conclusions: The detection of high level of seroreactivities against orthoebolaviruses in rural Cameroon, where no outbreaks have been reported, raises the possibilities of silent circulation of orthoebolaviruses, or of other not yet documented filoviruses, in these forested regions.

Article's main point: Our study found high seroreactivities to Ebola and Sudan orthoebolavirus antigens in rural Cameroonian populations, especially among Pygmies, despite no reported outbreaks. This suggests potential silent circulation of orthoebolaviruses or unknown filoviruses, highlighting the need for further surveillance and research.

Keywords: Cameroon; Central Africa; Ebola virus; Filoviridae; Sudan virus.

Figure 1.

Geographic distribution of participants from the 2 serological studies on orthoebolaviruses in rural Cameroon. Geographical location and number of individuals included in the 2 serosurveys on orthoebolaviruses in Cameroon. The case-control study on nonhuman primate (NHP) bites (in blue) included 795 people from South, East, and Centre regions: 265 people bitten by a NHP and 530 controls, adjusted on age, sex, ethnic group, and location. The second study (in red) was carried out in 2 rural villages in East Cameroon and included 691 people. Google Earth satellite imagery was used as the map background (Map data ©2024 Google). Maps realized with QGIS software.

Figure 2.

Average immunoglobulin G response against Ebola virus (EBOV) and Sudan virus (SUDV) glycoproteins (GPs) measured by surface plasmon resistance. Comparison of antibody response on EBOV GP (A) and SUDV GP (B) between Ebola virus disease (EVD) survivors and participants in the serosurveys from Cameroon. Antibody binding titers, measured in resonance units, were obtained for 5 EVD survivors from Guinea, and 14 samples from the case-control study on nonhuman primate bites in Cameroon, including 10 seroreactive (positive) samples to EBOV or SUDV (at least 2 antigens), 3 indeterminate (reactive to only 1 SUDV or EBOV antigen, respectively), and 1 negative (without reactivity to any antigen). Among the 10 reactive samples, 6 are reactive to both EBOV and SUDV, 2 to SUDV only (indeterminate for EBOV), and 1 to EBOV only (indeterminate for SUDV). Detailed results are given in Supplementary Figure 8. Each sample was tested twice. Differences between EVD survivors and Cameroonian samples were assessed using the Mann-Whitney test. **P < .01. Abbreviations: EBOV, Ebola virus; EVD, Ebola virus disease; GP, glycoprotein; Ind., indeterminate; MIA, multiplex immunoassay; Neg., negative; ns, not significant; Pos., positive; RU, resonance units; SUDV, Sudan virus.

Figure 3.

Multiplex immunoassay (MIA) avidity index (%) for immunoglobulin G against orthoebolavirus antigens. MIA avidity index on Ebola virus (EBOV; A) and Sudan virus (SUDV; B) nucleoprotein and VP40 for 21 samples from the case-control study on nonhuman primate bites from Cameroon were tested, including 14 with reactivity to at least 2 antigens (2 to EBOV antigens, 5 to SUDV, and 7 to both EBOV and SUDV), and 7 negative samples (4 with indeterminate profiles [ie, only 1 reactive antigen] and 3 negative to all antigens). Five sera from EBOV survivors of the outbreak in 2014–2016 in Guinea were used as positive controls and are indicated with their labels in the figure. Abbreviations: AI, avidity index; EBOV, Ebola virus; EVD, Ebola virus disease; Ind., indeterminate; Neg., negative; NP, nucleoprotein; SUDV, Sudan virus; VP40, 40-kDa viral protein.