Ebola: a strain resurfaces five years later

What is the epidemic situation in Guinea?

Between 2013 and 2016, Guinea was affected by a severe epidemic that spread to several other countries. It was the first time that Ebola had raged outside of central Africa. WHO has identified 29,000 cases, including more than 11,300 deaths. With my colleagues, we set up a follow-up of former patients, who still suffered from various ailments. Some would come back weeks or months after leaving the treatment center complaining of pain, headaches or visual disturbances. In addition, some of these survivors also suffered from depression, in particular because they were stigmatized, lost their jobs, their friends, their families. There was a certain suspicion of these people who had survived an illness considered fatal.

Then, in January 2021, a new epidemic appeared, with 23 cases, including 12 deaths. It ended in June.

What is the link between the two epidemics?

We conducted a genomic analysis to determine the origin of the new epidemic. We have performed complete or near-complete sequencing of 11 genomes. The 2021 virus exhibited ten mutations characteristic of that of the 2013-2016 epidemic. It is therefore likely that the virus originated from a human reservoir rather than an animal reservoir.

In addition, the 2021 virus had 10 to 12 new mutations. Considering that five years separate the two epidemics, it is very little! In fact, in order to survive, a virus invades the cells of its host and hijacks the machinery to replicate itself. But RNA viruses, like Ebola, are very unstable and the risks of mutations during replication are quite high. With a normal rate of replication, the virus should have had more mutations. We can therefore rule out the hypothesis that for five years the virus spread quietly in the population, passing from one host to the next. Everything suggests that it was dormant in a host, a former patient or someone who was in contact with a patient and who did not develop symptoms. There was therefore reactivation of the virus, which led to its resurgence.

Is it a surprise?

We knew that the virus sometimes persisted in certain fluids (semen, breast milk) in former patients. Our follow-up and other studies have reported persistence of up to 500 or even 700 days. We also observed cases of reactivation of the virus during the 2013-2016 epidemic and in others in the Democratic Republic of the Congo.

What is exceptional here is the length of dormancy: five years! It remains to be understood why the virus reactivates. We are currently working on a lead: in former patients, the amount of antibodies targeting the Ebola virus decreases over time, which would allow dormant virus reservoirs to become active again.

What are the consequences of your study?

There is a need to reconsider the health policy and the long-term follow-up of survivors. We must also communicate with the population to avoid the stigmatization of former patients. In particular, the person at the origin of a next epidemic could be a former patient, but also a person who does not know he is carrying the virus in dormancy. It is a global problem, everyone is concerned. Finally, it is also urgent to develop treatments capable of eradicating the dormant virus.

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