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…