A rare strain of Ebola with no approved vaccine or treatment circulated undetected for weeks in conflict-hit northeastern Democratic Republic of Congo before killing at least 87 people.

The first case developed symptoms on April 24, creating a four-week detection delay that enabled extensive uncontrolled community transmission, Africa Centres for Disease Control and Prevention Director-General Jean Kaseya said in an online briefing Saturday.

About 336 potential cases have been reported, mainly in Mongbwalu and Rwampara health zones in Ituri province near the Ugandan border, with additional possible infections in the provincial capital Bunia, Kaseya said. Four deaths have been confirmed among laboratory-positive cases.

Laboratory testing by the National Institute for Biomedical Research in Kinshasa confirmed the outbreak is caused by the Bundibugyo strain. The virus has caused only two previous known outbreaks: in Uganda in 2007 and eastern Congo in 2012. The deaths and suspected cases in this cluster have already exceeded those of the previous two outbreaks of this type combined.

“Every single day this region is where we have more than 70% of disease outbreaks in Africa coming from,” Kaseya said. “This is why we need to cover the region, cover the continent, and I am calling upon partners” to support the countries most at risk.

Ebola is among the world’s deadliest infectious diseases, killing between roughly a quarter and almost 90% of infected people depending on the virus species and the medical care available. The Zaire strain, discovered in 1976 near the Ebola River in what is now the Democratic Republic of Congo, caused a devastating West African epidemic roughly a decade earlier and has received the most research funding, leading to licensed vaccines and treatments.

“Ebola Zaire is the one that got all the attention, for very good reasons,” said Susan McLellan, director of the biocontainment care unit at the University of Texas Medical Branch, in an interview. The development of medical countermeasures, including monoclonal antibodies and vaccines, is less advanced for Bundibugyo, she said.

Treatment options

Africa CDC and the World Health Organization convened scientific experts this week to review possible therapies and vaccines and discuss accelerated plans to study their effectiveness, including whether existing vaccines may offer cross-protection against different Ebola strains, said Shanelle Hall, Africa CDC’s principal adviser on management and operations.

Health officials are considering four potential Ebola treatments for use under randomized controlled trial protocols in Congo and Uganda, including monoclonal antibodies, Gilead Sciences Inc.’s remdesivir and an oral version of the antiviral, she said.

Discussions are ongoing with both governments, though no trials have started yet, Hall said. Laboratory research has suggested the strain may be more susceptible to the antiviral than Ebola Zaire.

Several vaccine candidates are also under review. While Merck & Co.’s Ervebo vaccine is being considered, most existing Ebola vaccines were developed for the Sudan and Zaire strains rather than Bundibugyo. Early-stage candidates targeting the Bundibugyo strain from groups including Oxford University and Moderna Inc. are also being assessed.

The Ervebo shot remains too expensive for routine use at about $98.60 per dose and also requires ultra-cold storage, complicating deployment in remote areas, Hall said. Work is underway on next-generation Ebola vaccines that would be easier to store, cheaper to produce and potentially protect against multiple Ebola strains, including Bundibugyo.

Uganda case

Uganda has also confirmed a Bundibugyo Ebola case in a Congolese patient who traveled across the border for treatment and died in intensive care in Kampala on May 14 after deteriorating with bleeding symptoms. Authorities said the body was transported back to Congo the same evening, highlighting the risk of cross-border transmission through movement of patients and infected remains.

WHO and Africa CDC are deploying additional epidemiologists, laboratory specialists and infection-control experts to Ituri while airlifting five metric tons of emergency supplies including testing equipment, protective gear and treatment materials.

The outbreak is unfolding in a remote part of eastern Congo more than 1,700 kilometers (1,100 miles) from Kinshasa. Security risks, poor roads, mining-related population movement and frequent cross-border travel complicate the response.

Mongbwalu sits in one of the nation’s gold-mining regions, where tens of thousands of people move between remote mining camps and nearby trading centers. The region is also affected by armed groups and weak infrastructure, complicating efforts to deliver medical supplies and conduct disease surveillance and contact tracing.

“To access Mongbwalu isn’t easy,” said Jimmy Munguriek, Congo director for advocacy group Resource Matters. “The road isn’t there.”

The area has only one main hospital, Munguriek said, adding that overcrowded mining settlements and constant movement of workers could accelerate transmission if the outbreak isn’t quickly contained.

The U.S. Embassy in Kinshasa warned American citizens Saturday not to travel to Ituri “for any reason,” underscoring concerns over security and limited medical infrastructure in the region.

Escalation potential

“These zones are full of people who come from everywhere to work in artisanal mining,” Munguriek said. Armed groups active in the area and distrust of health authorities could also hamper containment efforts, he said: “There’s a big risk things will get much worse.”

Congo’s Health Ministry said the presumed first case was a nurse who died at the Evangelical Medical Center in Bunia. Patients have presented with fever, weakness, vomiting and, in some cases, bleeding, according to WHO, which said several cases rapidly deteriorated and died.

Ebola spreads through direct contact with bodily fluids from infected people or contaminated materials. Transmission risks can rise sharply in settings where people lack reliable access to running water and sanitation, said McLellan, who worked in West Africa during the 2013-2016 Ebola epidemic.

“It takes a very small amount of material,” she said, describing how bodily fluids can remain on skin or surfaces when hand-washing and sanitation are limited.

Even so, experts stressed that Ebola doesn’t spread easily through casual contact and that the risk outside the region remains low.

“There is no documented sustained spread of Ebola outside Africa,” researchers from Imperial College London said in an analysis published Friday, noting that exported cases during the West African epidemic were rare and mostly involved healthcare workers.

Travel risks

Congo has extensive experience responding to Ebola outbreaks after battling more than a dozen epidemics over 50 years. The country’s last outbreak, declared over in December, was contained within weeks. Congo’s government said it is deploying rapid-response teams and urged residents to avoid contact with sick people, infected animals and bodily fluids, while thoroughly cooking meat, particularly bushmeat.

The outbreak comes as some global health experts warn that cuts to U.S. foreign aid and public health programs could weaken disease surveillance and emergency response capacity in fragile regions. A study published in Science Thursday found the abrupt withdrawal of USAID funding was associated with increased conflict in heavily aid-dependent parts of Africa.

Africa CDC said it is not recommending travel restrictions or border closures at this stage, arguing that effective public health measures such as testing, screening and contact tracing are more effective at limiting transmission.

Officials said earlier intervention around infected individuals could potentially have reduced cross-border spread between Congo and Uganda, underscoring the importance of rapid detection and containment rather than restricting movement.

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