A survivor of the massive 2014-2016 West African Ebola outbreak almost certainly triggered an outbreak currently underway in Guinea, according to a new genetic analysis, news that has landed like a bombshell in the community of researchers who study the dangerous virus.
The analysis suggests that a survivor of the historic Ebola outbreak continued harboring the virus at least five years after being infected, eventually transmitting it to someone. Previously, the longest an Ebola survivor was believed to have shed the virus was about 500 days.
“I was completely shocked,” Angela Rasmussen, a virologist affiliated with the Georgetown Center for Global Health Science and Security, told STAT.
The discovery was revealed in a genetic analysis of viruses from the current outbreak that was conducted by scientists from Guinea, the Institut Pasteur in Senegal, the University of Nebraska Medical Center, and the University of Edinburgh. It was posted online Friday.
The scientists compared several genetic sequences from the current outbreak — in which 18 people have been infected to date — with sequences from viruses collected during the West African outbreak. Given the long interval between the two events, the assumption had been that this new outbreak was triggered by a new spillover of Ebola viruses from nature. That wasn’t what researchers found.
“The new genomes are most closely related to five identical Ebola virus Makona variant genomes sampled in August 2014 from the same region,” the scientists reported. Makona is the name of the Ebola Zaire strain that caused the 2014-2016 outbreak.
The new viruses had a small number of mutations — roughly a dozen. That’s far fewer than what one would have expected if there had been ongoing but undetected transmission of the virus in the region.
On Twitter, Rasmussen noted that given the rate at which the Makona variant evolved during the 2014 to 2016 period, the current viruses would have been expected to have amassed hundreds of mutations.
“The results are quite remarkable,” said Mike Ryan, who heads the World Health Organization’s Health Emergencies Program. Ryan said that the rate at which the virus had changed was far slower than the rate at which the Makona strain evolved during the 2014-2016 outbreak.
He warned the news could lead to further stigmatization of Ebola survivors, if they are seen within their communities as possible long-term sources of the virus. “Survivors deserve our support,” Ryan said. “They’ve been to hell and back.”
He suggested the finding underscores the need for programs that support survivors and that include follow-ups on their health. It also highlights the need to learn more about the phenomenon known as “viral persistence.”
Jason Kindrachuk, an assistant professor of emerging diseases from Canada’s University of Manitoba, recently received a research grant to do just that; he will be working with survivors of the West African outbreak in Sierra Leone.
He, too, was dumbfounded by the finding. “There’s that lump-in-your-throat moment,” Kindrachuk admitted.
It’s been known for years that some survivors of Ebola harbor virus in their bodies for periods of time after their infection.
The virus hides in places where the immune system can’t ferret it out — the testicles of some infected men, occasionally in the eyeball, or in spinal fluid. In some rare cases, survivors suffer a relapse when the virus reactivates. A Scottish nurse who worked in Sierra Leone during the West Africa outbreak, Pauline Cafferkey, suffered three bouts of disease over a couple of years.
These wells of hidden Ebola in survivors can also on rare occasions infect other people. Transmission events typically involve a male survivor who infects a female sexual partner.
The working hypothesis is that this is what happened in the most recent case. But currently there aren’t enough details known about how this outbreak started to be able to trace back the event to a survivor of the earlier outbreak.
The first known case in the current Guinea outbreak was a nurse who became sick in mid-January and died on Jan. 28. A number of the subsequent cases were people who attended her funeral on Feb. 1. But there have been reports the nurse had cared for her mother, who had been sick before her.
Daniel Bausch, a veteran of multiple Ebola outbreaks, said that in most known cases where a survivor has infected another person, it’s been a man who passed the virus to a sexual partner in his semen. Finding a male who might have transmitted the virus to the nurse or her mother — or someone else before them — might not be doable at this point.
“Can we get that far back? I don’t know. The trail gets cold pretty readily when everybody’s dying,” said Bausch, director of the U.K. Public Health Rapid Support Team, a partnership between Public Health England and the London School of Hygiene and Tropical Medicine. “We may never know.”
Bausch noted that until the West African crisis — which was the first time Ebola transmitted in African cities — outbreaks were small, often only a few dozen cases. The West African outbreak involved more than 28,000 cases and over than 11,000 deaths.
Prior to that, the largest was in Gulu, Uganda, in 2000 and involved 425 people, which at the time was thought to be a hellishly large event.
But more recently, the northeastern corner of the Democratic Republic of the Congo endured a two-year battle with Ebola in an outbreak that recorded 3,470 cases and 2,287 deaths. Bausch said this new experience with large outbreaks — which leave large numbers of survivors — may be giving the world a chance to see something that it could never spot in outbreaks of 50 or 60 people that left only 20 or so survivors.
“Is this just that now we have a sample size that is big enough so that rare events, we’re catching [them]?” he wondered.