The Associated Press / A woman wearing a protective mask stands in the corridor of a hospital Sunday in Bunia, Congo.

KINSHASA, Congo — Congo will open three Ebola treatment centers in the eastern Ituri province, and the World Health Organization is sending a team of experts to the country, following an outbreak of a rare type of the virus that has killed nearly 120 people.

An American doctor in Congo is among the newly confirmed cases of the virus with no approved vaccines or medicines, Congolese officials said Monday, as details emerged about the government’s delayed response to the outbreak.

The WHO on Sunday declared the Ebola outbreak a public health emergency of international concern. As of Monday, there were over 118 deaths and 300 suspected cases in Ituri and North Kivu provinces, and one death and one suspected case in neighboring Uganda. Experts say the number of cases is likely to rise as health officials conduct more surveillance.

The Bundibugyo virus spread undetected for at least a few weeks, health experts and aid workers said. Cases have now been confirmed in Bunia, North Kivu’s rebel-held capital of Goma, Mongbwalu, Butembo and Nyakunde.

“Because early tests looked for the wrong strain of Ebola, we got false negatives and lost weeks of response time,” said Matthew M. Kavanagh, director of the Georgetown University Center for Global Health Policy and Politics. “We are playing catch-up against a very dangerous pathogen.”

He criticized the Trump administration’s earlier decision to withdraw from the WHO and make deep cuts in foreign aid — “the exact surveillance system meant to catch these viruses early,” he said.

The severity of the symptoms and the rising caseload are fueling a growing sense of panic in the neighborhoods of Bunia.

“I know the consequences of Ebola, I know what it’s like,” said Noela Lumo, a resident of Bunia. She previously lived in Beni, a region hit by former Ebola outbreaks. As soon as she heard about the latest outbreak, Lumo began making protective masks by hand.

Congo has said the first person died from the virus on April 24 in Bunia, and the body was repatriated to the Mongbwalu health zone, a mining area with a large population.

“That caused the Ebola outbreak to escalate,” said Congo’s health minister, Samuel Roger Kamba.