DAKAR (Reuters) – Scientists in Sierra Leone have found live bats infected with Marburg virus, a deadly hemorrhagic fever similar to Ebola and so far undetected in West Africa, a U.S. government statement said on Thursday.

The African fruit bat is the reservoir host of the virus, which has caused at least 12 outbreaks of hemorrhagic fever on the continent.

Angola suffered the worst epidemic in 2005, when 90 percent of the 252 people infected in the southern African country died. The continent’s most recent outbreak killed three people in Uganda last year.

In a statement on Thursday, the U.S. Centers for Disease Control and Prevention (CDC) said five Egyptian rousette fruit bats caught in Sierra Leone tested positive for the Marburg virus.

No human cases of the fever have so far been reported, although the presence of infected bats — who do not show obvious signs of the disease — increases the risk of contracting the virus.

“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,” said CDC ecologist Jonathan Towner in the statement.

Symptoms and signs of Marburg include headache, vomiting blood, muscle pains and bleeding through various orifices. Transmission occurs through contact with infected body fluids and tissue, which bats shed when they feed on fruit.

Sierra Leone was hit by West Africa’s worst Ebola outbreak, which ran from 2013 and 2016 and killed at least 11,300 people in Guinea, Liberia and Sierra Leone.

(Reporting by Sofia Christensen; editing by Martyn Herman)