Serologic Prevalence of Ebola Virus in Equatorial Africa

Abstract

We conducted a serologic survey of 2,430 serum samples collected during 1997-2012 for various studies to determine the prevalence of the hemorrhagic fever virus Ebola virus (EBOV) in equatorial Africa. We screened serum samples for neutralizing antibodies by using a pseudotype microneutralization assay and a newly developed luciferase immunoprecipitation system assay. Specimens seroreactive for EBOV were confirmed by using an ELISA. Our results suggest a serologic prevalence of 2%-3.5% in the Republic of the Congo and the Democratic Republic of the Congo, which have reported outbreaks of infection with EBOV. In addition we detected a seroprevalence of 1.3% in southern Cameroon, which indicated a low risk for exposure in this region.

Keywords: Cameroon; Democratic Republic of the Congo; ELISA; Ebola virus; Ghana; Republic of the Congo; Uganda; equatorial Africa; filovirus; hemorrhagic fever; hemorrhagic fever virus; luciferase immunoprecipitation system; neutralization assay; pseudotypes; serologic prevalence; viruses.

Figure 1

Numbers of serum samples collected from Ghana, Cameroon, Republic of the Congo, DRC, and Uganda in study of serologic prevalence of Ebola virus in equatorial Africa. DRC, Democratic Republic of the Congo.

Figure 2

High-throughput screening data for neutralizing antibodies against EBOV and MACV glycoprotein pseudotypes in serum samples in study of serologic prevalence of Ebola virus in equatorial Africa. A) Uganda; B) Cameroon; C) Ghana; D) southern Cameroon; E) Republic of the Congo; F) Kinshasa, Democratic Republic of the Congo; G) Kasaï Oriental Province, Democratic Republic of the Congo. Serum samples were tested at a 1:50 dilution against the different pseudotypes. Samples that reduced pseudotype infectivity by >50% compared with a negative serum control were considered positive and confirmed by titration. Error bars indicate 95% CIs. EBOV, Ebola virus; MACV, Machupo virus.

Figure 3

Antibody reactivity against Ebola virus matrix protein as measured by luciferase immunoprecipitation system assay for the different sample sets in study of serologic prevalence of Ebola virus in equatorial Africa. Data were normalized against individual cutoff values determined for each experiment. Samples yielding reactivity >1 were counted as positive specimens. Error bars indicate 95% CIs. 1, Uganda 2007; 2, Cameroon 2007; 3, Ghana 2007; 4, Cameroon 2011–2012; 5, Republic of the Congo; 6, Kinshasha, Democratic Republic of the Congo; 7, Kasaï Oriental Province, Democratic Republic of the Congo.

Figure 4

Summarized Ebola virus nucleoprotein ELISA data for confirmation of neutralizing and LIPS-reactive specimens across all sample sets in study of serologic prevalence of Ebola virus in equatorial Africa. For comparison, 57 random nonneutralizers were included. The ELISA cutoff value of 4.62 U/mL (dashed line) was determined on the basis of background reactivity for 47 serum samples from the local general population. Error bars indicate 95% CIs. LIPS, luciferase immunoprecipitation system.

Figure 5

Overlap of different assay results for Ebola virus serology across all samples in study of serologic prevalence of Ebola virus in equatorial Africa. A) Total sample set; B) sample sets from Kinshasha, Democratic Republic of the Congo; C) sample set from Kasaï Oriental Province, Democratic Republic of the Congo. LIPS, luciferase immunoprecipitation system; NA, not applicable (ELISA was performed only for samples with positive results in other assays); NP, nucleoprotein; VP40, matrix protein.