Risk Factors Associated with Ebola and Marburg Viruses Seroprevalence in Blood Donors in the Republic of Congo

Background Ebola and Marburg viruses (family Filoviridae, genera Ebolavirus and Marburgvirus) cause haemorrhagic fevers in humans, often associated with high mortality rates. The presence of antibodies to Ebola virus (EBOV) and Marburg virus (MARV) has been reported in some African countries in individuals without a history of haemorrhagic fever. In this study, we present a MARV and EBOV seroprevalence study conducted amongst blood donors in the Republic of Congo and the analysis of risk factors for contact with EBOV. Methodology and Findings In 2011, we conducted a MARV and EBOV seroprevalence study amongst 809 blood donors recruited in rural (75; 9.3%) and urban (734; 90.7%) areas of the Republic of Congo. Serum titres of IgG antibodies to MARV and EBOV were assessed by indirect double-immunofluorescence microscopy. MARV seroprevalence was 0.5% (4 in 809) without any identified risk factors. Prevalence of IgG to EBOV was 2.5%, peaking at 4% in rural areas and in Pointe Noire. Independent risk factors identified by multivariate analysis were contact with bats and exposure to birds. Conclusions/Significance This MARV and EBOV serological survey performed in the Republic of Congo identifies a probable role for environmental determinants of exposure to EBOV. It highlights the requirement for extending our understanding of the ecological and epidemiological risk of bats (previously identified as a potential ecological reservoir) and birds as vectors of EBOV to humans, and characterising the protection potentially afforded by EBOV-specific antibodies as detected in blood donors.
Author Summary Ebola and Marburg viruses cause haemorrhagic fevers often fatal to humans. Here, we looked for antibodies to Ebola and Marburg viruses (i.e., markers of previous contact with these viruses) in Congolese blood donors with no previous history of haemorrhagic fever. We found serologic evidence for contact with Marburg and Ebola viruses in 0.5% and 2.5% of blood donors, respectively. The circulation of Marburg virus occurs at a very low rate without any identified risk factor. In contrast, prevalence to Ebola virus was peaking at 4% in rural areas and in Pointe Noire city. Importantly, we identified that contacts with bats and birds constituted two independent environmental determinants of exposure. This study confirms that contact with Ebola virus is not infrequent in Congo and can occur in the absence of haemorrhagic fever. It highlights the requirement for further investigating the role of bats and birds in the ecological cycle of Ebola, and for determining whether asymptomatic contact with Ebola virus can provide subsequent protection against severe forms of the Ebola disease.