Ebola is one of the most terrifying viruses known to scientists, largely because it’s so deadly but also because it presents with such gruesome symptoms, including projectile vomiting, extreme diarrhea and profuse, uncontrolled bleeding.
The most recent Ebola outbreak infected more than 28,600 people and killed more than 11,300—and though the epidemic has subsided, a recent study reveals an unsettling finding: People can get Ebola and not know they have it. In the report, published in the journal PLOS Neglected Tropical Diseases, researchers from the health group Partners In Health (PIH), which provided medical aid during the Ebola outbreak, wanted to know whether there were people who contracted the disease but did not show any symptoms of it.
“The majority of viruses that infect humans cause a range of disease, from asymptomatic infection to severe disease and death,” says study author Dr. Eugene Richardson, a PhD candidate in anthropology at Stanford. “So we thought, why should Ebola virus be any different?”
Richardson and his co-authors, including PIH co-founder Paul Farmer, tested 187 people in the 900-person village of Sukudu in Sierra Leone for evidence that they had been infected with Ebola. Of the people tested, they found that 14 had Ebola-related antibodies in their blood, which means they been infected at some point with the virus. What stunned the researchers, however, was that none of these 14 people were included in the original tally of 34 local residents who had contracted the virus.
“Because minimally symptomatic individuals were not vomiting or having diarrhea, it is highly unlikely they were a source of significant viral transmission,” says Richardson, noting that what makes Ebola so contagious is the bodily fluids that can be hard to avoid by those people close to those infected. “However, they still represent an instance where the health system failed to prevent human-to-human transmission of virus.”
The report suggests that many instances of Ebola transmission between people may have gone unidentified during the outbreak. It also suggests that Ebola has a wider variety of symptoms, which could have implications for how outbreaks are dealt with in the future.
“Our efforts at containment may have been much less successful than is currently appreciated,” says Richardson. “We should continue to conduct research with the goal of improving patient care and prevention of virus transmission in future outbreaks.”