A research team headed by Stanford University scientist Eugene Richardson has identified twelve individuals with previously undetected Ebola virus infection in a ‘hotspot’ village in Sierra Leone, approximately one year after the village outbreak.
Colorized scanning electron micrograph of filamentous Ebola virus particles (blue) budding from a chronically infected cell (yellow). Image credit: NIAID / CC BY 2.0.
An estimated 10-80% of people who show symptoms of Ebola virus disease die, depending on their access to intensive care.
However, scientists have also seen some evidence that a minority of people may catch the Ebola virus without developing symptoms.
During the 2013-2016 outbreak, however, these so-called ‘minimally symptomatic infections’ were not considered epidemiologically relevant to models, projections, or intervention efforts so were not studied or tracked in detail.
From October 2015 through January 2016, a year after the peak of the Ebola epidemic, Dr. Richardson and co-authors conducted a survey of people living in Sukudu, Kono District, Sierra Leone, a village of 900 inhabitants which had been a major ‘hotspot’ of Ebola.
The researchers identified 193 adults and children over age 4 who had lived with or shared a latrine with a confirmed case of Ebola during the period of active transmission but were never identified as Ebola virus disease cases.
They collected blood from 187 of these individuals. They then tested the blood samples — as well as positive and negative controls from known Ebola cases and people not exposed to the virus — for Ebola glycoprotein antibodies, the presence of which indicates a past Ebola infection.
Of the 187 exposed individuals, none of whom were previously known to have Ebola virus disease, the team identified 14 who tested positive for Ebola antibodies.
Two of these 14 admitted having a fever while being quarantined, while the other 12 denied any signs or symptoms.
“The findings provide further evidence that Ebola, like many other viral infections, presents with a spectrum of clinical manifestations, including minimally symptomatic infection,” Dr. Richardson and his colleagues said.
“These data also suggest that a significant portion of Ebola transmission events may have gone undetected during the outbreak.”
The findings were published this week in the journal PLoS Neglected Tropical Diseases.
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E.T. Richardson et al. 2016. Minimally Symptomatic Infection in an Ebola ‘Hotspot’: A Cross-Sectional Serosurvey. PLoS Negl Trop Dis 10 (11): e0005087; doi: 10.1371/journal.pntd.0005087
