GENEVA (AP) — A top official at the World Health Organization said that a genetic analysis of the ongoing Ebola outbreak in Guinea suggests it may have been sparked by a survivor of the devastating West Africa epidemic that ended five years ago.

At a press briefing in Geneva, WHO emergencies chief Dr. Michael Ryan described the results of the genetic sequencing of the virus in Guinea as “quite remarkable.”

Scientists in Africa and Germany posted their results on a virology website on Friday, concluding that the current Ebola virus sickening people in Guinea is extremely similar to the virus that sparked the widespread West Africa outbreak that began in 2014.

“More studies are going to be needed,” Ryan said. But he added that based on the available genetic sequencing data, the current outbreak was unlikely to be linked to an animal — which is how nearly all previous Ebola epidemics have begun. “(This) is much more likely to be linked to a persistence (of virus) or latency of infection in a human.” Ryan said that would probably be the longest period of time that a virus has ever persisted between outbreaks.

Scientists have previously documented Ebola survivors who inadvertently infected others long after they had recovered, but such rare cases have not prompted outbreaks. In 2018, doctors published a study about a Liberian woman who probably caught Ebola in 2014 but then infected three relatives about a year later.

Health officials have also warned that men can sometimes infect others via sexual activity long after they seem to have recovered — the virus can persist in semen for more than a year.

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The rare possibility of Ebola spreading long after infection highlights the importance of monitoring survivors, and Ryan cautioned against their stigmatization. He said that the vast majority of people who are sickened by Ebola clear the virus from their system and recover within six months.

Ryan said a tiny proportion of people end up carrying the virus, but are not infectious to others “except in very particular circumstances.”

He said there are 18 cases of Ebola in Guinea to date and that WHO has sent more than 30,000 vaccine doses to the country.

The Ebola outbreak that swept across West Africa from 2014 to 2016 ultimately killed more than 11,000 people.