By Billy Stockwell, Sana Noor Haq, CNN

(CNN) — The chief of the World Health Organization said Tuesday he is “deeply concerned about the scale and speed” of the deadly Ebola outbreak in the Democratic Republic of Congo (DRC) and Uganda, as questions swirl over how the virus spread undetected for several weeks.

As of Tuesday, there have been 131 deaths linked to the outbreak, according to the DRC’s health minister, Dr. Samuel Roger Kamba, with more than 500 cases suspected.

WHO Director-General Dr. Tedros Adhanom Ghebreyesus said 30 cases have so far been confirmed in DRC’s northeastern Ituri province.

The outbreak, driven by the Bundibugyo virus, is one of several viruses known as Orthoebolaviruses that can cause Ebola disease, is mainly hitting the remote Ituri province, Tedros said.

Meanwhile, in neighboring Uganda, two laboratory-confirmed cases have also been reported in the capital, Kampala, according to WHO.

Ebola has an average fatality rate of 50%, according to WHO. The disease is spread through direct contact with the bodily fluids of an infected person, according to Africa Centres for Disease Control and Prevention (Africa CDC). It can also be passed through contact with contaminated materials or a person who has died from the disease.

There are currently no approved treatments or vaccines specific to the Bundibugyo virus. Medical workers are trying to develop a monoclonal antibody therapy as a potential treatment, Dr. Satish Pillai, a deputy director in the Division of Preparedness and Emerging Infections at the US Centers for Disease Control (CDC), told reporters on Monday, without stating a timeline.

War, displacement stifle relief efforts

Regional aid and health officials say years of war, crippling aid cuts and acute malnutrition in parts of the DRC have ultimately hindered response efforts to the outbreak – after the latest viral flare tore through communities in Ituri province.

One relief staffer warned children are “most vulnerable” in the wake of the outbreak. Philippe Guiton, the national director for the UK-based non-profit World Vision in the DRC, said they are “already heavily affected by conflict and where humanitarian assistance remains insufficient due to lack of resources.”

The east zone director at World Vision, David Munkley, added that, “Ituri is already facing an alarming situation of acute malnutrition, which further weakens people’s immune systems, combined with extremely limited access to healthcare in remote areas.”

Later Tuesday, Tedros also highlighted the province of Ituri as highly insecure. “Conflict has intensified since late 2025, and fighting has escalated significantly over the past two months, resulting in civilian deaths,” Tedros told an emergency committee.

More than 100,000 people have been “newly displaced,” he said, adding, “high levels of population movement” may “increase the risk of further spread.”

US Secretary of State Marco Rubio conceded that areas in the DRC where cases had been reported were “a little tough to get to.” “It’s in a rural area, so it’s kind of confined in a hard to get to place in a war-torn country, unfortunately,” the diplomat told a group of reporters at the State Department Tuesday, in his first remarks since the outbreak.

Others voiced concern over why authorities took so long to identify and track initial cases, following a string of Ebola outbreaks in the past several years. The largest outbreak transpired in West Africa from 2014 to 2016, when 11,325 people died and more than 28,600 people were infected, according to WHO.

“I’ve been saying the most concerning thing to me has been how much we learned, how quickly we learned it,” Craig Spencer, a doctor who survived an Ebola infection in 2014, told CNN on Monday. “There’s no doubt that this is probably much worse than what we think right now. I suspect the true case total is much higher than what’s being reported.”

In response to the growing epidemic, the US invoked a public health law on Monday to limit entry into the country from the affected region, just as one US national tested positive for the strain in the DRC. The American citizen is being transported to Germany for treatment at Berlin’s Charité university hospital, the German health ministry said Tuesday.

Ugandan authorities sought to reassure visitors on Tuesday, insisting there has been no local transmission within the country despite the two cases, which the Uganda Tourism Board said were involving Congolese nationals “who entered Uganda from the DRC.”

The Africa CDC criticized the US’ travel restrictions, saying “broad travel bans can disrupt lives and economies.”

Later Tuesday, the State Department warned Americans against all travel to the DRC, South Sudan and Uganda, and to reconsider travel to Rwanda due to the outbreak in the region.

When did the epidemic start?

The first known suspected case was a health worker, whose symptoms started on April 24, according to WHO. The person later died at a medical centre in Bunia, the capital of Ituri province.

Then, on May 5, WHO received an alert about an “unknown illness” with high mortality in the province, the agency said. After an investigation by a “rapid response team” on May 13, the outbreak was confirmed as Bundibugyo virus on 15 May.

Jeremy Konyndyk, former lead for COVID and disaster relief at the US Agency for International Development (USAID), said multiple “generations of transmission” must have gone undetected before the outbreak was confirmed, which he said was a “big, big problem.”

On Sunday, the UN health body declared the epidemic a “public health emergency of international concern,” and said the high positivity rate and increasing number of cases and deaths point toward “a potentially much larger outbreak.”

Tedros said this is the first time a director-general has declared an emergency of this kind before convening the committee later Tuesday.

Anne Ancia, WHO’s representative in the DRC, confirmed Tuesday the outbreak has also spread to the country’s North Kivu province, which directly borders Ituri province, but added there is still “significant uncertainty” about the true number of infections.