Scientists have identified a new variant of the Ebola-causing Bundibugyo virus behind the 2026 outbreak in the Democratic Republic of the Congo (DR Congo) and Uganda, according to a study published in Nature Medicine on Monday.

Bundibugyo strain is not new: variants of the pathogen caused outbreaks in Uganda in 2007-2008 and the DR Congo in 2012. However, researchers found that the strain circulating in 2026 began with a new transmission of the virus from an animal to humans, rather than the re-emergence of strains responsible for previous epidemics in the region. The animal source remains unknown.

The conclusion is based on an analysis of 22 viral genomes obtained from infected people in the DR Congo and Uganda, which formed a distinct genetic cluster separate from variants linked to the previous outbreaks.

The researchers called for broader local diagnostic capacity and expanded genomic surveillance to detect future outbreaks earlier.

Bundibugyo virus, or BDBV, belongs to the same group of viruses as the better-known Zaire ebolavirus and can cause severe Ebola disease. That form of the virus is carried by fruit bats and spreads through direct contact with infected animals or bodily fluids from infected individuals. Symptoms of Bundibugyo strain include fever, severe headaches, muscle and body pain, weakness, fatigue, sore throat, vomiting, diarrhea, stomach pain, and loss of appetite.

The World Health Organization (WHO) has described the current virus as the largest Ebola epidemic ever recorded in the DR Congo, surpassing the 2018-2020 outbreak. The agency’s Director-General Tedros Adhanom Ghebreyesus warned last week that the disease was spreading faster than efforts to contain it. 

The outbreak had spread across 53 health zones in five provinces of the DR Congo as of August 10, with Ituri remaining the main epicenter, according to the country’s Health Ministry. The authorities have recorded 4,449 confirmed cases and 2,061 deaths, putting the fatality rate at 46.3%. 

Neighboring Uganda, meanwhile, declared itself Ebola-free last month after recording 20 cases, 15 of which were imported from the DR Congo. Two people died and 18 recovered.