A new Ebola virus outbreak in Guinea appears to have been sparked by a person who was first infected during the country’s previous epidemic five years ago, suggesting persistent infections in survivors could be a source of future outbreaks.
Recentpreliminaryanalyses of viral genome sequences by N’Faly Magassouba at the Gamal Abdel Nasser University of Conakry in Guinea and his colleagues, along with other research teams, revealed that the virus responsible for the current cases hardly differs from the strain that caused the previous epidemic. This indicates the virus may have lain dormant in someone who caught it in 2016.
“This is very surprising and very shocking,” says César Muñoz-Fontela at the Bernhard Nocht Institute for Tropical Medicine in Germany, who was in Guinea during the previous Ebola epidemic. “It’s like a relapse.”
Read more: Guinea is swiftly vaccinating people to contain latest Ebola outbreak
There were 28,646 reported cases during the 2013-2016 Ebola epidemic in west Africa and 11,323 reported deaths. These new findings indicate that some of the people who survived could still harbour the virus years later and potentially pass it on to others.
“What does that mean for [Ebola virus disease] survivors?” says Magassouba. He fears the new findings will worsen existing stigmatisation of these people.
Researchers already knew that Ebola could persist in the body for a long time, but five years is unprecedented, says Muñoz-Fontela. In 2016, a resurgence of the 2013-2016 epidemic in Guinea was traced back to a survivor who shed the virus in their semen for at least 531 days after first becoming infected, and transmitted it to their partner.
It is possible that the virus behind the current outbreak in Guinea may have persisted in a person’s body before being transmitted in a similar way, says Muñoz-Fontela.
Read more: Ebola virus has lurked in a man’s semen for more than 500 days
In addition to semen, Ebola can also persist in other so-called immune-privileged sites in the body – those parts that are difficult for the immune system to reach – such as cerebrospinal fluid in the central nervous system or fluid in the eye called the vitreous humour.
The first known Ebola virus outbreak was in the Democratic Republic of the Congo in 1976, but the 2013-2016 outbreak in West Africa was much larger, which could explain why more cases of persistent infections in survivors have been detected in recent years. It might be that this is relatively rare, so it is only becoming apparent now that there are larger numbers of survivors, says Muñoz-Fontela.
Another possibility, he says, is that viral persistence is an inadvertent consequence of an increased availability of treatments. “Now we have [treatments] that can save people [who] in the past were impossible to save – and when you have persons with that amount of virus in the blood, the treatment itself may push the virus to these immune-privileged sites.”
Screening for persistent Ebola virus infections and vaccinating the contacts of Ebola virus disease survivors could help to protect people and prevent future outbreaks, says Magassouba, although availability of vaccines could be a limiting factor. As of 16 March, there had been 18 cases and 9 deaths in the new outbreak in Guinea, with 366 contacts of cases identified and 3332 people vaccinated.