Marburg virus, a deadly cousin of Ebola virus, has been found for the first time in bats in west Africa, U.S. researchers said Thursday.

The discovery means Marburg is a threat in west Africa — where a giant epidemic of Ebola infected 28,000 people and killed 11,000 of them in 2014-2016. The region is crisscrossed by roads and paths and people travel across borders to towns and cities, making it easier to spread outbreaks of infectious disease. Usually outbreaks of Ebola and Marburg are in isolated regions and have been less likely to spread.

The knowledge that Marburg lives in bats in Sierra Leone can help officials prepare for potential outbreaks, the researchers said.

“Five Egyptian rousette fruit bats tested positive for active Marburg virus infection. Scientists caught the bats separately at locations in three health districts: Moyamba, Koinadugu and Kono,” the Centers for Disease Control and Prevention, which led one of the expeditions that found the infected bats, said in a statement.

“There have been no reported cases of people sick with Marburg in Sierra Leone, but the virus’s presence in bats means people nearby could be at risk for contracting Marburg virus. Marburg virus is a cousin to Ebola virus that causes a similar, often fatal disease in people.”

Both Marburg and Ebola are terrifying because, depending on the strain and availability of medical help, they kill as many as 90 percent of victims. They can cause a hemorrhagic fever that causes internal and external bleeding, as well as severe diarrhea and vomiting that lead to shock.

The Egyptian fruit bat has been known to carry Marburg. It’s a reservoir, meaning the animals can carry and spread a virus, but it doesn’t make them sick. Bats are reservoirs for many viruses, including Marburg, rabies and middle east respiratory syndrome virus or MERS.

A mother cries for her child, who died of Ebola in Beni, Democratic Republic of Congo, on Dec. 17, 2018. Goran Tomasevic / Reuters

“We have known for a long time that rousette bats, which carry Marburg virus in other parts of Africa, also live in West Africa. So it’s not surprising that we’d find the virus in bats there,” said ecologist Jonathan Towner, who led the CDC team. “This discovery is an excellent example of how our work can identify a threat and help us warn people of the risk before they get sick.”

Three people died in an outbreak of Marburg in Uganda a year ago. In 2005, a big outbreak of Marburg in Angola killed 90 percent of the 252 people infected.

There’s a large cave full of fruit bats in Uganda where people, including tourists, have caught Marburg. “In eastern and central Africa, these bats can roost in colonies of more than 100,000 animals. However, the colonies of Egyptian fruit bats identified in Sierra Leone so far have been much smaller, which may explain why there have not been any known Marburg virus disease outbreaks in this country,” the CDC said in a statement.

Bats can spread viruses by biting people, but their saliva and guano can also spread the viruses — for instance, when they forage on fruit that people also gather and eat. People can catch viruses when they hunt and eat bats, as well.

Marburg’s relative, Ebola, is more common and may also be spread by bats. The Democratic Republic of Congo in central Africa is now fighting a very big outbreak of Ebola. At least 549 people have been infected in the outbreak and 326 have died, the World Health Organization said Thursday. At least 50,000 people have been vaccinated against the virus but civil war has made it difficult for health workers to do their jobs. The virus has also spread in towns, making it hard to contain.