EbolaPeople with Ebola may not always show symptoms

Published 21 November 2016

A research team determined that 25 percent of individuals in a Sierra Leone village were infected with the Ebola virus but had no symptoms, suggesting broader transmission of the virus than originally thought. These individuals had antibodies to the virus, suggesting they had been infected at one time — yet said they had had no symptoms during the time of active transmission in the village. Theresearch confirms previous suspicions that the Ebola virus does not uniformly cause severe disease, and that people may be infected without showing signs of illness.

A year after the Ebola epidemic in West Africa, researchers from the Stanford University School of Medicine and other institutions identified fourteen individuals previously unknown to have had the disease in a Sierra Leone village that was an Ebola hot spot.

These individuals had antibodies to the virus, suggesting they had been infected at one time. Yet twelve said they had had no symptoms during the time of active transmission in the village.

Stanford says that the research confirms previous suspicions that the Ebola virus does not uniformly cause severe disease, and that people may be infected without showing signs of illness, said Gene Richardson, MD, a former fellow in the Division of Infectious Diseases and Geographic Medicine at Stanford who is now a Ph.D. candidate in anthropology at the university. The findings also suggest that the epidemic was more widespread than previously believed. Based on the results of the study, the researchers calculated the prevalence of minimally symptomatic infection to be 25 percent.

“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 said. “It provides important evidence on that front. It also means a significant portion of transmission events may have gone undetected during the outbreak. This shows there was a lot more human-to-human transmission than we thought.”

The study was published online in PLOS Neglected Tropical Diseases. The study also was presented 14 November at the American Society of Tropical Medicine and Hygiene’s annual meeting in Atlanta. Richardson is lead author of the study, and Paul Farmer, MD, Ph.D., a Harvard professor and director of Partners In Health, is the senior author.

Testing individuals
The research was done in the rural village of Sukudu in Sierra Leone, a country where Richardson and his colleagues cared for hundreds of patients in Ebola treatment units managed by Partners In Health.

The village, with about 900 residents, had been one of three major hot spots in the Kono District, in the eastern part of the country, during the heat of the Ebola crisis between November 2014 and February 2015. There were thirty-four reported cases of Ebola in the village, including twenty-eight deaths.

More than 28,000 cases of Ebola infection were reported in Africa during the epidemic, the largest and longest in history. More than 11,000 people are estimated to have died because of the disease.