U.S. health officials are preparing to screen passengers flying in from Rwanda for symptoms of Marburg virus, a severe infection similar to Ebola.

Amid an outbreak of Marburg virus in Rwanda, travelers coming into the United States who have been in Rwanda in the previous 21 days will be screened starting next week, the US Department of Health and Human Services announced Monday.

Marburg has caused small, episodic outbreaks since first being identified, most recently last year in Tanzania and Ghana. It is one of the deadliest known viruses, with no approved vaccines or specific treatments.

Marburg virus disease has killed 11 people and sickened 25 others in Rwanda, which declared an outbreak on Sept. 27.

The East African country continues to investigate the source of the outbreak, first traced among patients in health facilities.

In Rwanda, 11 deaths have been reported from this rare but deadly disease. Two people tested negative in Germany this week.

The advisory has been elevated from Category 2 to Category 3 on a scale of 4, indicating a strong recommendation to do not travel.

Health officials in Rwanda are dealing with the country’s first outbreak of the Marburg virus, an Ebola-like disease which, if left untreated, has a fatality rate of up to 88%.

As health officials work furiously to stem the spread of Marburg virus in Rwanda, U.S. health officials announced Monday that all passengers flying from that country to the United States will soon be screened for the often deadly disease.

The CDC will begin screening some travelers for Marburg virus disease. Rwanda has reported 49 cases and 12 deaths from MVD.