Over 40 people have died in a growing Ebola outbreak in the Democratic Republic of the Congo and Uganda, where government and international aid organizations are struggling to cope with the spread of the disease.

The current strain of Ebola, the Bundibugyo virus, is “a severe and often fatal form” of the disease, according to the World Health Organization. It has no approved treatment or vaccine.

The World Health Organization and the Africa Centers for Disease Control and Prevention both reported 43 confirmed deaths across the countries as of Saturday, including 42 in Congo and one in Uganda, according to the WHO. However, 349 people are suspected to have died from the virus in Congo and Uganda.

There are 272 confirmed cases of the disease in both countries, with 263 in Congo and nine in Uganda, the WHO reported. The Africa CDC has reported a total of 263 confirmed cases across Congo and Uganda, with more than 1,100 suspected cases still under investigation.

The source of the virus is believed to be the fruit bat, and human infection can occur through contact with secretions from infected wildlife, according to the WHO. It then spreads from person to person through the same method, and can be amplified by burial practices that involve contact with the deceased and inadequate infection prevention and control in healthcare settings.

Doctors Without Borders is one of the organizations helping respond to the outbreak in Congo’s Ituri province. Deputy Director Alan Gonzalez said the team is playing catch-up with the disease.

“The virus is spreading faster than we’ve been able to respond,” Gonzalez told NBC News, adding that “correct testing” is key.

“It’s really difficult to know who is positive, who has the virus, who doesn’t. And then it’s harder to do contact tracing,” he said.

Gonzalez said the outbreak has the potential to become even worse due to the “perfect storm” of a delay in identifying the Bundibugyo strain and its quick spread.

On Saturday, WHO Director-General Tedros Adhanom Ghebreyesus visited the city of Bunia in Congo, the epicenter of the outbreak in the country’s Ituri province. Tedros advised against unsafe burial practices and urged countries to reconsider travel bans and border closures, saying they “discourage transparency.”

Tedros said Sunday that five patients in Bunia had recovered from the disease, The Associated Press reported. He spoke about the patients’ good prognosis during the opening of a new Ebola treatment center in the city.

“Of course we’re still working on vaccines and treatments, but that doesn’t mean that people cannot recover from Ebola,” he said, according to the AP.

Congo has had multiple Ebola outbreaks — this one is its 17th. Tedros said Saturday that the country has always been able to end each outbreak.

“That history gives me real confidence,” he said.