Ebola can hide in humans for years before killing again, new research finds

New genetic research appears to confirm fears scientists had about a deadly Ebola outbreak in Guinea in February: The source of the outbreak was likely the dormant remains of the virus in a survivor who caught it at least five years earlier. The discovery could complicate efforts to contain the emerging viral disease.

At the end of January 2021, a 51-year-old nurse in the West African country contracted Ebola (formerly known as Ebola virus disease, or EVD). Like many victims, she initially experienced vague symptoms such as headache, nausea, and general weakness. Although she was hospitalized, her doctors unfortunately mistakenly diagnosed her with malaria and salmonella infection, and she was sent home after two days. She fell ill again at home and died three days later.

After her death, her husband and other family members who attended her funeral also fell ill and four of them eventually died. These cases finally alerted the national health authorities. In mid-February, blood samples confirmed the outbreak and health workers rushed to get it under control. Between February and June 2021, when the outbreak was officially declared over, 16 confirmed cases were reported, along with 12 deaths.

Typically, Ebola outbreaks begin with zoonotic transmission from an infected animal to a person, with some bats considered the primary host of the virus. But the first analyzes of the first blood samples taken from the victims during this outbreak suggested that something else was going on. The virus observed in their blood closely resembled a variant collected from survivors of the 2013-2016 Ebola outbreak in West Africa, the largest and deadliest outbreak of the virus to date, with more than 11 000 deaths. Soon scientists suspected the virus had somehow reappeared from a human host years later and was killing again.

This new study, published Wednesday in the wild, anything but seals that seem to be right. Researchers in Guinea, France and Germany performed next-generation genetic sequencing of the virus collected from 12 victims of the outbreak, using it to build complete or nearly complete genomes of the virus. They then used this information to build a family tree of the strains and compared it to the virus that was floating about five years ago.

The virus found in Guinea this year was indeed closely related to the virus seen in the previous outbreak in West Africa, the authors said, indicating “that the new outbreak was not the result of a new event in West Africa. overflow of an animal reservoir “. Additionally, they did not find any signs of a large genetic divergence between then and now, which suggests that it was not heavily transmitted between humans during this time. Instead, the source virus may have caused a persistent but slow infection with reduced reproduction in a survivor, or it may have become completely latent and then reactivated for some unknown reason, making the survivor contagious again.

Scientists have known since the outbreak in West Africa that the virus can survive unnoticed in victims for some time after they have fully recovered, especially in pockets of the body where the immune system is less active, such as the eyes or semen. But the longest known delay between someone contracting the virus and passing it on to someone else or becoming ill again, before that, was around a year and a half. A much wider window for transmission of the virus means communities may be more vulnerable to future outbreaks than currently believed. It can also make the lives of survivors, who already tend to experience discrimination and prejudice from others, even more difficult, the perpetrators warn.

“The human origin of the 2021 EVD epidemic, and the associated change in our perception of the emergence of EBOV, calls for special attention to survivors of the disease,” they wrote. “The fear that survivors will be stigmatized as a source of danger needs careful attention. “

In this case, it is possible that unknown patient zero transmitted the virus during sexual intercourse. But since the first new victim was a nurse, the patient may also have experienced a recurrence of symptoms which led to a health care visit and transmission at this point. The nurse herself may have had a dormant infection return, although this is less likely, as she had no documented cases before.

Overall, the authors say these findings should fuel research to find a way to keep survivors virus-free and protect communities after an outbreak subsides.

“In addition to the importance of appropriate health measures focused on survivors, the late resurgence of the virus also highlights the urgent need for further research into potent antiviral agents that can eradicate the reservoir of latent virus in patients with the disease. of EVD, and on effective vaccines that provide long-term protection, ”they wrote.