Evaluating the frequency of asymptomatic Ebola virus infection

Placide Mbala, Marc Baguelin*, Ipos Ngay, Alicia Rosello, Prime Mulembakani, Nikolaos Demiris, William Edmunds, Jean Jacques Muyembe

*Corresponding author for this work

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    The potential for asymptomatic infection from Ebola viruses has long been questioned. Knowing the proportion of infections that are asymptomatic substantially changes the predictions made by mathematical models and alters the corresponding decisions based upon these models. To assess the degree of asymptomatic infection occurring during an Ebola virus disease (EVD) outbreak, we carried out a serological survey in the Djera district of the Equateur province of the Democratic Republic of the Congo affected by an Ebola outbreak in 2014. We sampled all asymptomatic residents (n = 182) of 48 households where at least one case of EVD was detected. To control for potential background seroprevalence of Ebola antibodies in the population, we also sampled 188 individuals from 92 households in an unaffected area with a similar demographic background. We tested the sera collected for anti-Ebola IgG and IgM antibodies at four different dilutions. We then developed a mixture model to estimate the likely number of asymptomatic patients who developed IgM and IgG responses to Ebola antigens in both groups. While we detected an association between medium to high titres and age, we did not detect any evidence of increased asymptomatic infection in the individuals who resided in the same household as cases. This article is part of the themed issue ‘The 2013–2016 West African Ebola epidemic: data, decision-making and disease control’.

    Original languageEnglish
    Article number20160303
    JournalPhilosophical transactions of the Royal Society of London. Series B, Biological sciences
    Issue number1721
    Publication statusPublished - 26 May 2017

    Bibliographical note

    Funding Information:
    This study was funded by the Fischer Family Trust (A.R.) and the National Institute for Health Research Health Protection Research Unit in Immunisation at the London School of Hygiene and Tropical Medicine in partnership with Public Health England (M.B.). The views expressed are those of the authors and not necessarily those of the funders. This study was also made possible by the generous support of the American people through the United States Agency for International Development (USAID) Emerging Pandemic Threats Program-2 PREDICT-2 (Cooperative Agreement no. AID-OAA-A-14-00102). The contents are the responsibility of the authors and do not necessarily reflect the views of USAID or the United States Government. We are grateful to Dr Passy Bosomba, medical district officer of the Boende Health District, for his support during our fieldwork, Ioannis Ntzoufras from the Athens University of Economics and Business for assistance with the multivariate mixture model, Stefan Flasche and Judith Glynn from the London School of Hygiene and Tropical Medicine for useful discussions, Geoff Soule and Gary Kobinger at Public Health Canada for advice on the serological assay and reagents. We were also allowed to use the Metabiota laboratory to conduct our analysis when the INRB had problems with the electricity.

    Publisher Copyright:
    © 2017 The Author(s) Published by the Royal Society. All rights reserved.


    • Asymptomatic infection
    • Ebola virus disease
    • Household survey
    • Serology


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