The recent Ebola outbreak emerged from an infected person 5 years earlier

A large international research group today published an article suggesting that Ebola viruses can break out of five years of dormancy to trigger a new outbreak of infections. While this is not the first time Ebola has reappeared in a previously infected individual, the new findings significantly extend the duration of the risk.

At present, we have few ideas on how and where the virus persists in the human body. But there are now tens of thousands of people who have survived previous infections, so this is an area where more research is urgently needed.

A re-epidemic

The African nation of Guinea has experienced a small Ebola outbreak that began in January 2021 when a nurse fell ill. Due to a misdiagnosis, she was not immediately isolated, allowing the virus to spread. Fortunately, a major outbreak that occurred in the same region from 2013 to 2016 allowed local health authorities to obtain sophisticated diagnostic equipment, including real-time RT-PCR machines that are used for testing. COVID-19. This ultimately allowed authorities to determine Ebola as the cause of his illness, identify 15 more cases and take action to end the outbreak. A total of 12 of the 16 infected have died.

In order to better understand the source and spread of the outbreak, samples from these patients were used to obtain the genome of the virus causing the outbreak. This method makes it possible to compare the sequence of the genome with that of previous epidemics and of samples taken from bats, which may also carry the virus. An evolutionary analysis can then suggest how the first patient got infected.

But in this case, the analysis produced a strange result. All the cases regrouped into a small group that belonged to the group of viral variants that caused the 2013-2016 epidemic in the same region. These cases included mutations that had only occurred during the previous outbreak and were not found in any bat populations.

In itself, this result is not entirely shocking. It is possible that the virus is circulating at low levels in isolated populations without attracting the attention of health authorities. If he had to, however, he would continue to pick up mutations. But the strain behind the 2021 outbreak didn’t look much different from the one circulating in 2016. It’s as if it had spent much of the intervening period frozen in time.

Suspended animation

For the 2021 strain to have picked up so few mutations since the 2013-2016 epidemic, its normal mutation rate would have had to be divided by five. The alternative is that, as in the previously mentioned case, the virus remained dormant in a person who recovered from an infection during the previous outbreak. The virus has been found in seminal fluid for up to 500 days after infection cleared, and there has been at least one case of transmission after this time. But the new outbreak would require more than three times as long a dormancy.

Previous studies suggest that this type of persistence is rare. But there are currently over 17,000 survivors of the previous outbreak, so there is certainly an opportunity for a rare event to occur.

At the moment, however, we have no idea what Ebola tissue might be hiding in, let alone the mechanism that allows it to go to sleep. The only RNA viruses known to cause long-lasting infections (called retroviruses) do so by integrating a DNA copy of themselves into the genome of their host. But Ebola doesn’t seem to have the genes to do it.

The obvious solution is to work with Ebola survivors to check for persistent infections, which could be incorporated into a more general surveillance program given the apparent risk of long-term dormancy. But this poses its own challenges. Ebola survival is stigmatized in many communities hard hit by the virus, those who survived their infections often lose their jobs and homes. It will therefore not necessarily be easy to recruit people to work with the research community on this project.

The situation may be changing, however, as two Ebola vaccines have recently been approved for use and more are being tested; they have been deployed to help contain epidemics in recent years. Along with the changing public health situation in Africa, these vaccines could also begin to change the social perception of those infected.

Nature, 2021. DOI: 10.1038 / s41586-021-03901-9 (About DOIs).