New Study Reveals Zoonotic Origin of Fast-Moving Ebola Outbreak in DRC

The Ebola outbreak currently ravaging the Democratic Republic of the Congo (DRC) was caused by a new transmission from animals to humans rather than by variants linked to earlier outbreaks, according to a new study published in the medical journal Nature Medicine.

The virus in eastern DRC has killed more than 2,000 people of 4,449 recorded cases, making it the fastest-moving Ebola outbreak on record. It was formally declared on May 15 , though genetic sequencing later revealed the virus had actually begun circulating in February.

On Wednesday, the World Health Organization (WHO) said the current Bundibugyo strain of the Ebola virus is spreading faster than health authorities can contain it and is on track to become the deadliest outbreak on record.

So what have scientists discovered about how it was transmitted to humans? And can it be contained?

Here’s what we know:

What does the new study say about this Ebola outbreak?

In a report published this week in the medical journal Nature Medicine, researchers from the DRC, Uganda, Belgium and other countries analysed the genetic make-up of virus samples from 22 patients in the DRC and Uganda. They found that the outbreak strain was genetically distinct from previous Bundibugyo Ebola viruses seen in outbreaks in 2007 and 2012.

The report suggested that the virus began with a new animal-to-human transmission incident, which then spread to other people.

The animal source has not been specified but the researchers said the outbreak in Uganda was linked to the outbreak in the DRC.

Earlier, health officials in the region said the outbreak is being driven by the rare Bundibugyo strain of the virus, for which no vaccine has yet been developed.

Krutika Kuppalli, an infectious diseases doctor with experience in Ebola and outbreak response, explained that the study citing a “new animal transmission” as the reason for the outbreak, does not mean that a new form of Ebola has suddenly emerged or that animals are now transmitting the virus differently.

“What the genomic data suggest is that the current outbreak began with a new ‘zoonotic spillover’ event – meaning the virus likely crossed independently from an animal reservoir into a person – rather than resulting from continued circulation or re-emergence of virus from a previous human outbreak,” she said.

“After that initial spillover, the outbreak has been driven predominantly by human-to-human transmission,” she added.

How dangerous is this strain of Ebola?

On Wednesday, WHO Director-General Tedros Adhanom Ghebreyesus said that at its current pace, the current Ebola outbreak is on track to eclipse the West African outbreak of 2014 to 2016. That crisis killed at least 11,300 people of a reported 28,600 cases and accelerated the push to develop a vaccine.

That was a different strain of the Ebola virus known as Zaire and the vaccine developed then does not work for the current strain, which is spreading.

Dr Abdirahman Mahamud, WHO’s director for health emergency alert and response operations, said the agency’s moderate projection has the outbreak peaking within six months. Under a more severe scenario, it could stretch on for nine to 12 months.

“Beyond the zoonotic spillover event from animals to humans, it is the human-to-human transmission dynamics of the Bundibugyo virus that make it dangerous,” Kaja Abbas, associate professor of infectious disease epidemiology and dynamics at the London School of Hygiene & Tropical Medicine and Nagasaki University, told Al Jazeera.

Dr Kuppalli also emphasised that the way this strain of the virus was initially transmitted to humans does not make it intrinsically more dangerous.

How is it treated?

Kuppalli said the animal origin of the virus does not change required treatment.

“Once someone develops Ebola disease, management is based on the virus causing the illness and the patient’s clinical condition, not whether their infection ultimately originated from an animal or from another person. What matters here is that Bundibugyo virus (BDBV) currently does not have the same licensed, proven virus-specific therapeutics that we have for Zaire ebolavirus,” she said.

“Supportive care, which includes aggressive fluid and electrolyte management, treatment of shock and organ dysfunction, and management of co-infections, remains critical, while investigational therapeutics are being evaluated,” she added.

“Ebola outbreaks have historically begun through zoonotic spillover. The bigger concern is what it tells us about our preparedness: we still do not fully understand where and when these spillover events will occur, making prevention and early detection extremely difficult.”

“In this outbreak, there also appears to have been substantial transmission before the outbreak was recognised, which gave the virus an opportunity to establish multiple chains of transmission,” she added.

What can be done to contain this outbreak?

Researchers who worked on the new study said increasing “decentralised laboratory diagnostics capacity, including genomic sequencing capacity and timely detection ” could help pre-empt future outbreaks.

Clinicians are also working to develop treatments.

“While no licensed treatments or vaccines exist today, experimental therapeutics and vaccines are in the clinical development pipeline that are specifically targeted towards the strains of the Bundibugyo virus currently circulating in the ongoing Ebola outbreak in the DRC and Uganda during 2026,” Abbas said.

While a vaccine against the latest strain is being developed, a WHO official said in May that medical supplies, including personal protective equipment (PPE) ⁠⁠to prevent Ebola, were being sent to ⁠⁠the DRC.

“We have sent 12 tonnes of supply. An additional six are arriving. These include personal protective equipment for ⁠⁠front-line health workers [and] samples,” Anne Ancia, WHO representative in the DRC’s Ituri province, told media in May.

At the forefront of the fight to break the spread in the DRC are health workers who have been treating patients while also dealing with the risk of becoming infected themselves.

More than 100 health workers have been infected and about 35 have died.

The response to the outbreak has been further complicated by several factors, including strikes by unpaid health workers, misinformation and cultural traditions. These have included open-casket family burials of some of those killed by the virus, potentially increasing the risk of further transmission.

Kuppalli said better Ebola preparedness is required, not just focusing on stopping transmission once an outbreak has been recognised.

“We also need much stronger health surveillance at the human-animal interface, broader diagnostics capable of detecting different Ebola viruses and medical countermeasures that work across Ebola species,” she said.

“This outbreak is showing us the consequences when the virus gets a several-month head start.”

How have other countries responded?

Many countries have raised concerns about the latest Ebola virus outbreak and some, such as Bahrain, have suspended entry for 30 days for foreign travellers arriving from South Sudan, the DRC and Uganda.

Neighbouring countries, including Rwanda and Uganda, have introduced measures to prevent the virus from crossing their borders.

Rwanda imposed health restrictions, including barring entry to foreign travellers who had been in the DRC in the previous 30 days.

The US warned that travellers, including US citizens, who have been in the DRC within 21 days before departure will not be allowed to board commercial flights to US destinations.

Governments across Asia have also begun introducing border screening and bolstering quarantine preparedness.