Scientists Discover a Sixth Species of Ebola Virus in Bats

Scientists have discovered a previously unknown species of Ebola virus, called Bombali virus, that's carried by at least two species of bats in Sierra Leone. This is the first Ebola virus species detected in an animal before having been detected in humans.

Although researchers believe the virus is capable of infecting humans, it's unclear if it would cause disease.

The Bombali virus joins the five already-known Ebola virus species: Zaire virus, Bundibugyo virus, Sudan virus, Ta? Forest virus and Reston virus. Of those five, all except the Reston virus are known to cause severe and often fatal disease in humans. [The 9 Deadliest Viruses on Earth]

The most devastating Ebola outbreak in recent history was caused by the Zaire virus and lasted from 2013 to 2016 in Guinea, Sierra Leone and Liberia. In that time, more than 28,000 people were infected with Ebola and 11,325 died. And the current Ebola outbreak, which started in early August in the North Kivu province of the Democratic Republic of Congo, is also caused by the Zaire virus, according to the World Health Organization.

The source of Ebola viruses has been tricky for scientists to pin down, even after four decades of research. (The virus was discovered in 1976, according to the Centers for Disease Control and Prevention.) The reservoir, or organism that the viruses naturally live and reproduce in, is still unknown. Previous research has made a strong case that bats are the primary reservoir species, but until now, scientists have been unable to isolate and recover a complete Ebola virus genome from bats.

So, in an effort to identify Ebola viruses in their host species before the virus spreads to humans, scientists with the U.S. Agency for International Development's (USAID) PREDICT Ebola Host Project collected biological samples from 535 animals in Sierra Leone — 244 bats, 46 rodents, 240 dogs and five cats — and tested them for the presence of Ebola viruses.

"If you want to prevent Ebola outbreaks, it's important to know which species are hosts and can shed the virus," Tracey Goldstein, co-lead study author and an associate director of the One Health Institute at the University of California, Davis, said in a statement. "Then, we can help target changes in behavior [in those animals], so we can protect people, which is the overarching goal of our work."

In the study, the scientists found four bats that tested positive for an Ebola virus; all other animals tested negative. These bats were captured inside three human dwellings within 12 miles (20 kilometers) of one another, where livestock and crops were being raised for local consumption. Three of the bats were little free-tailed bats (Chaerephon pumilus) and one was an Angolan free-tailed bat (Mops condylurus). Both species are widely distributed across Africa and often roost together.

When the team sequenced the genome of the bat-dwelling Ebola virus, the researchers found that the virus was different enough from previously identified Ebola viruses to represent a new species. The researchers named the new species after the location where they first detected it: the Bombali district of Sierra Leone.

Although the Bombali virus has been detected only in bats thus far, the scientists identified a binding protein that would facilitate the transfer of the virus into human cells, suggesting that human infection is possible. But even if the virus is able to infect humans, there's no evidence that it will cause any symptoms. It's unclear whether the Bombali virus will behave more like the Reston virus, which doesn't cause disease in humans, or the Zaire virus, which causes severe disease.

The authors of the study pointed out that the purpose of their work is not to incite panic or a fear of bats. These animals play an important role in the ecosystem as insectivores, pollinators and seed dispersers, the authors wrote. Previous studies showed that killing bats doesn't reduce disease transmission but instead can increase the number of susceptible bats and enhance disease transmission. 

By Kimberly Hickok