Lurking among survivors, the Ebola virus may wake up and cause a new epidemic

At the end of January 2021, the specter of Ebola resurfaced in southern Guinea. This formidable virus, responsible for haemorrhagic fevers which kill three to nine times out of ten, had already struck this country and its neighbors between 2013 and 2016. At the time, nearly 29,000 cases had been diagnosed and 11,300 people had died in Guinea, Liberia and Sierra Leone, for the most part.

Quickly identified, the 2021 epidemic ended in June, after affecting 23 people and causing 12 deaths in Guinea alone. Disturbingly, the affected region was only 200 kilometers from the epicenter of the massive 2013-2016 epidemic. Where did this new home come from? Did the virus pass from a wild animal (a monkey, for example) to the human species, as it did in the previous epidemic? Hunters, in close contact with the fauna of this forest region, are often the first targets of this virus.

The emergence of the new Guinean cluster, in fact, results from the awakening of a viral strain that was dormant in a survivor of the last epidemic. That’s what reveals a study published, September 15, in the review Nature.

Read also Ebola: after new analyzes, “no proof” of the resurgence of the virus in Côte d’Ivoire

A small number of mutations observed

The authors sequenced the genome of the Ebola virus in twelve patients affected at the start of the transmission chain, from the end of January 2021. As a result, the viral strain found in them was the same as that which caused the 2013 epidemic. -2016. Only a very small number of mutations which have appeared in the meantime have been observed.

“This means that the virus that caused this new outbreak has remained lurking, in a dormant form, in the bodily fluids (semen, breast milk, urine, aqueous humor of the eye, etc.) of a survivor of the previous epidemic. And that he suddenly woke up, five to seven years later, to provoke this cluster ”, explains Martine Peeters, virologist at the French Development Research Institute (IRD) and co-author of the study. This survivor has not been identified, but this conclusion is solid. Genomic analyzes, in fact, were confirmed by three laboratories: the Guinea Infectious Disease Research and Training Center (Cerfig), with the help of the IRD and the Robert-Koch Institute in Berlin, the laboratory of the Guinea Haemorrhagic Fevers Project, with the Bernhard-Nocht Institute of Tropical Medicine in Hamburg, and the Pasteur Institute in Dakar.

This is a surprise. Until now, we knew that the virus could sleep eighteen months in an Ebola survivor. Ebola outbreaks from survivors have already been reported in the Democratic Republic of Congo (DRC). However, never had such a long period of dormancy been observed. This awakening of the virus, from former infected people, worries all the more that there are, in West Africa, tens of thousands of Ebola survivors. Another challenge: infected subjects are sometimes asymptomatic.

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