The latest Ebola outbreak may have started with someone infected years ago

The ongoing Ebola outbreak in Guinea was most likely sparked by someone infected during the outbreak seven years ago, a new study shows. Viruses from both outbreaks are almost genetically identical, hinting that the virus did not jump from an animal to people, as scientists expected, but that it had lurked hidden in a human body for years.

“With this news, I was really, really shocked,” says Angela Rasmussen, a virologist with Georgetown University in Washington, D.C.

Potential cases of Ebola began emerging in the West African nation in late January, and Guinean health officials declared an outbreak on February 14 after three people tested positive for the virus. The region hadn’t seen an outbreak since the one in 2013–2016, which claimed over 11,000 lives. A separate, unrelated outbreak in the Congo was declared on February 7.

As of March 6, 29 cases and 13 deaths had been reported in both countries, according to Africa Centres for Disease Control and Prevention. A genetic analysis found that four viruses from people infected in the Guinea outbreak were the close relatives of viruses that had infected people in 2014, according to a trio of preliminary reports posted March 12 at virological.org. Only about a dozen mutations separate these new cases from the 2014 cases. That’s far fewer than the more than 100 mutations scientists expect would accumulate over that period if there were sustained transmission of the virus.

The lack of mutations suggests that the newest outbreak did not get its start when a bat virus jumped into humans and began spreading. Rather, the most recent cases appear to be a resurgence of the same strain that caused the 2013–2016 Ebola outbreak, carried by someone who was infected back then.

Researchers have known that Ebola virus can stick around in the body after recovery. Some cases in West Africa during the 2013–2016 outbreak stemmed from individuals who had been infected and had recovered months, or even more than a year, earlier. But the new findings show the most recent outbreak began after a five-year lull in cases and suggest that the virus wasn’t replicating during that time, meaning the virus may have gone dormant.

The finding “suggests some sort of weird mechanism that hasn’t been seen before,” Rasmussen says, but doesn’t mean that Ebola outbreaks from dormant viruses in humans are going to be happening all the time. Right now, what might have happened is “a mystery. We’ll probably solve [the mechanism], but right now there’s just not very much known about it.”

Other recent research backs up the idea that Ebola can lie low in the body for years. Immune proteins that recognize the virus spiked in the blood in 39 out of 51 people months after those people recovered, molecular virologist Georgios Pollakis and colleagues reported in the Feb. 18 Nature. Though the team could not find evidence in the blood that the virus was replicating, the roused immune response hints that the virus could be hiding somewhere in the body.

“We were quite surprised to see [that] data,” says Pollakis, of the University of Liverpool in England.

For Pollakis, the new developments emphasize the need for continued surveillance and research on diseases that aren’t top-of-mind. “The biggest lesson is that public health needs serious investment,” Pollakis says. “We focus on what is [spreading] faster, on the biggest player. And then we leave the virus that doesn’t seem to be a burden for the moment… now it comes back to haunt us.” 

Though experts say transmission of the virus from people infected long ago appears to be rare, the outbreak raises fears that Ebola survivors could face new stigmas.

Health officials have sprung into action across the region to isolate potential contacts in the current outbreak and vaccinate them and their contacts, a strategy known as ring vaccination (SN: 5/18/18). In Guinea, about 500 contacts have been identified, and over 1,600 people vaccinated as of March 5.

Still, public health officials may need to alter Ebola vaccination strategies, Rasmussen says. While the current strategy is to control outbreaks with ring vaccination, “we need to think about maybe having a mass immunization campaign — not using vaccination as a control strategy but as a prevention strategy.”