WASHINGTON — Scientists have found evidence of the deadly Ebola virus in a bat in Liberia, the first time the virus has been found in a bat in West Africa, researchers and officials announced Thursday.
A team of scientists working with the government of Liberia presented their findings in Monrovia, the Liberian capital. The discovery represents a major step forward in understanding where human Ebola cases come from, one of the biggest unanswered questions surrounding these outbreaks, said Jonathan Epstein, a scientist with EcoHealth Alliance, a global nonprofit that is part of the research team.
No human cases of Ebola are linked to this discovery, scientists said. Liberia has had no new human cases since the end of the 2014-2016 epidemic that devastated West Africa, killing more than 11,000 people in Liberia, Guinea, and Sierra Leone.
Bats have long been suspected of being a natural reservoir or animal host for Ebola, meaning the virus can live and grow inside the animals without harming them. But more than 40 years and over two dozen outbreaks after Ebola emerged in Central Africa, researchers still don’t know what animal or animals carry it, much less how it spreads to people.
‘‘It’s been really difficult to get definitive evidence,’’ Epstein said.
The findings add to evidence suggesting that bats could serve as the natural wildlife carrier for Ebola, scientists said. The team found genetic material from the virus and antibodies in the bat’s blood, indicating the animal’s immune response against infection.
But Epstein and others cautioned that much more research is needed. Scientists tested samples taken from 150 Mineopterus inflatus bats in northeastern Liberia. But only one of those bats tested positive, Epstein said.
If this species of bat, known as the Greater Long-fingered bat, turns out to be a natural host for the virus, scientists would expect to find more than one bat with antibodies against the virus, he said. It’s also possible the bat became infected by another bat species living in the same habitat, he said.
The Mineopterus inflatus bats live in caves, mines, and forests and eat insects. They are about the size of a small mouse, with about a 12-inch wing span.
Other experts said much more study is required to know whether this bat species is a natural host.
‘‘It’s not unuseful information, but it’s not altogether convincing of reservoir status,’’ said Tom Ksiazek, a virologist at the University of Texas Medical Branch at Galveston, who specializes in hemorrhagic fever viruses, such as Ebola.
‘‘It’s a step in the right direction,’’ Ksiazek said. ‘‘This suggests that certainly, the virus is naturally occurring in the ecology of West Africa.’’
Most experts say the natural animal host for Ebola is some type of fruit bat, not one that eats insects, he said. Previous evidence of Ebola in bats has all been in fruit bats, Ksiazek said. Most notable is that a tiny fruit bat, Rousettus aegyptiacus, has been found definitively to be the animal host of Marburg virus, a close and equally fearsome cousin to Ebola.
Scientists are writing a research paper about their discovery. But Liberian officials did not want to wait for publication, which can take a year, before releasing the information, Epstein said. Officials want to use the information to reinforce a public health message to Liberians to avoid bats to prevent potential infection. Bats can excrete virus in their saliva, urine, and feces. The animals are also a common food source; handling or eating infected animals can also spread the virus.
The West Africa Ebola epidemic began with a single transmission from an animal to a 2-year-old boy in a remote village in Guinea, according to the World Health Organization. Scientists still don’t know exactly how the child became infected, but researchers say it probably involved contact with wild animals. Before he became sick, he was seen playing near a hollow tree heavily infested with bats, according to a 2015 WHO report on the epidemic.
Scientists at Columbia University’s Mailman School of Public Health, which is part of the team, are working to determine whether the virus found in the bat is the exact same virus that caused the West Africa epidemic and the current Ebola outbreak in Congo, the second-largest ever recorded. There had been at least 713 cases and 439 deaths as of Wednesday, according to Congo’s health ministry.