In the heat of the Ebola crisis in late 2014, Stanford’s Gene Richardson, MD, was among the brave physicians who volunteered in Sierra Leone to help treat hundreds of patients with the devastating disease. At that time, Ebola infection was viewed by many as a death sentence.
Since then, however, Richardson and his colleagues have gone back to the West African country to do further testing and study in one village that was a “hot spot” during the epidemic. There, they found additional people who tested positive for the virus but said they’d never been ill during the epidemic.
That suggests Ebola infection does not always lead to severe disease and death — sometimes it may cause only mild symptoms or none at all.
“The study corroborates previous evidence that Ebola is like most other viruses in that it causes a spectrum of manifestations, including minimally symptomatic infection,” Richardson, a medical anthropologist, told me for our press release. The research appears today in PLOS Neglected Tropical Diseases.
Based on testing done in one village of 900 people, Richardson and his colleagues estimated the incidence of asymptomatic infection to be 25 percent. That is a remarkably high figure, suggesting transmission of the disease was probably far greater than once thought. More than 28,000 cases were reported during the epidemic, including 11,000 deaths due to the disease, according to the World Health Organization.
Richardson said it’s not known whether someone who is asymptomatic can pass along the virus. Typically, the virus is spread through vomiting, diarrhea or virus-laden blood – routes of exposure that are unlikely in someone without active disease. There have been documented cases of individuals transmitting the virus through sexual contact, even long after they have recovered from severe illness. Whether that might be a pathway for transmission by an asymptomatic individual isn’t known, Richardson said.
He and his colleagues are continuing to work in Sierra Leone, especially in areas where surveillance was poor, to get a better sense of how many people were impacted during the crisis. In the meantime, he said the study “reminds us that we need to do a much, much better job in future epidemics.”
Previously: Ebola: It's not over, All hands on deck: Doctor answers call to work on largest Ebola epidemic in history and From bedside to patient: an Ebola survivor's remarkable journey
Image of Ebola virus particles by NIAID