An American doctor working with a medical missionary organization in the Democratic Republic of the Congo has tested positive for Ebola, the Centers for Disease Control and Prevention and the missionary group said Monday.

The individual was being taken to Germany for treatment, the CDC said.

There are more than 250 suspected cases and 80 suspected deaths so far in the Ebola outbreak in the Congo and neighboring Uganda, the World Health Organization said. The WHO declared the outbreak a global health emergency on Sunday.

The missionary group Serge said Dr. Peter Stafford tested positive for the Bundibugyo ebolavirus variant after being exposed while treating patients at Nyankunde Hospital, in the Congo city of Bunia, where he has served since 2023. His wife, who is also a doctor with the aid group, and another physician remain asymptomatic, the group said.

"All three medical professionals have strictly adhered to established quarantine protocols since the potential exposure," Serge said in a statement on its website.

Six other Americans, in addition to Stafford, are expected to be moved out of the region to ensure they can be monitored or treated, the CDC said Monday.

Sources previously told CBS News that at least six Americans have been exposed in the outbreak.

The first suspected case in this outbreak was a health worker who reported symptoms starting on April 24 and died at a medical center in Bunia, the WHO said.

Since then, suspected cases have grown significantly and crossed country borders. Several factors, including the location of the outbreak — an urban area with significant population mobility — and attacks by armed groups in the region, have health officials concerned about further spread.

The outbreak is only the third known outbreak of the Bundibugyo strain, one of the viruses that causes Ebola disease. Unlike the more common Zaire strain, there is no vaccine or treatment for this strain, which was first discovered in Uganda in 2007.

Ebolaviruses are transmitted from person to person through bodily fluids such as vomit, blood or semen. Initial symptoms of the disease include fever, fatigue, muscle pain, headache and sore throat. As the disease progresses, symptoms include vomiting, diarrhea, abdominal pain, rash, organ dysfunction and sometimes internal or external bleeding, the WHO said.

Because it spreads through close contact, family members, caregivers and medical personnel can be at high risk from exposure to sick patients.

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