The World Health Organization issued an alert Tuesday after the Congolese government confirmed an outbreak of Ebola fever, a highly fatal disease that has no cure or treatment.

The Associated Press reports that the Congolese government placed an area in southeastern Congo under quarantine Tuesday, after tests confirmed that several persons were infected with the virus.

Spokesman Toussaint Tshilobo announced the quarantine and said experts from Medecins Sans Frontieres are already treating patients, but more help was needed. The World Health Organization issued an alert Tuesday, urging more doctors to travel to Congo and help contain the spread of the virus.

The WHO said five samples of blood had tested positive for Ebola, while nearly 40 other samples are pending.

The United States’ Centers for Disease Control and Prevention and a lab in Gabon confirmed the disease as a hemorrhagic fever, and specifically as Ebola, Health Minister Makwenge Kaput said on national television Monday.

More than 100 people have already died in the area, but specialists think some of the deaths may have been caused by a virus called Shigella.

Gregory Hartl, a spokesperson for the WHO, said some of the patients responded to anti-biotics, which have no effect against the Ebola virus. The AP reports that patients who have Shigella are at high risk of being contaminated with Ebola, as there is no isolation within the hospital.

“It wouldn’t be surprising if something else was going on,” Hartl said. “But because Ebola is involved, we have to be on high alert.”

The villages affected are situated between the towns of Mweka and Luebo. Some 200 miles away is Kitwit, the city where Ebola last struck in Congo before the current outbreak. In 1995, 245 people died there.

Ebola is highly contagious and is transmitted through contact with the blood or secretions of an infected person. In severe cases, victims hemorrhage to death. More than half of those infected die.

Symptoms include vomiting, diarrhea, internal and external bleeding, fever, nausea, headache.

The first United Nations teams arrived Sunday night with protective equipment, Hartl said.