Largest Bundibugyo Ebola Outbreak on Record Reaches 534 Confirmed Cases, Spreads to Uganda

The Bundibugyo Ebola outbreak in eastern Democratic Republic of the Congo has become the largest documented outbreak of that Ebola species, with confirmed cases now spread across two countries and officials warning that it is unusually difficult to bring under control. The World Health Organization said in a Disease Outbreak News update published June 8, with data as of June 6, that DRC had recorded 515 confirmed cases and 91 confirmed deaths, while Uganda had 19 confirmed cases, including two confirmed deaths, plus one probable death. That put the combined total at 534 confirmed cases and 93 deaths.

What sets this outbreak apart is not only its scale but the limits of the tools available to fight it. There are no licensed vaccines or specific treatments for Bundibugyo ebolavirus, a rarer Ebola species than the better-known Zaire strain. WHO and the U.S. Centers for Disease Control and Prevention have said vaccines and monoclonal antibody treatments approved for Zaire ebolavirus are not expected to work against Bundibugyo. The response was also slowed early on because some standard rapid Ebola tests used in field laboratories target the Zaire strain and initially returned negative results, forcing samples to be sent to DRC’s national reference laboratory for PCR testing and genomic sequencing.

DRC officially declared the outbreak on May 15, after WHO said it had first been alerted on May 5 to an unknown high-mortality illness in Mongbwalu Health Zone in Ituri province. The earliest known suspected case had symptom onset on April 24. Genomic sequencing at DRC’s national reference laboratory confirmed Bundibugyo ebolavirus on May 15, according to WHO. Two days later, WHO declared the outbreak in DRC and Uganda a Public Health Emergency of International Concern, its highest level of global alarm. On May 18, the Africa Centres for Disease Control and Prevention declared a Public Health Emergency of Continental Security. “Today, we declare this PHECS to mobilise our institutions, our collective will, and our resources to act swiftly and decisively,” Africa CDC Director-General Jean Kaseya said at the time.

Uganda’s cases have been linked to cross-border transmission from DRC, underscoring how quickly the outbreak moved beyond Ituri. WHO also said one case involved travel through the United Arab Emirates and that it was coordinating contact tracing with Uganda and the UAE. Previous Bundibugyo outbreaks were recorded in Uganda in 2007 and in DRC in 2012, but WHO says the current event is the largest yet documented for this Ebola species.

The center of the outbreak, Ituri province, poses major operational problems for responders. WHO says insecurity, population displacement and highly mobile mining communities are obstructing surveillance, case finding and contact tracing. The agency also reported infections among health workers and early deaths that pointed to lapses in infection prevention and control, including four health workers who died within four days in Mongbwalu. In an outbreak where isolation and rapid tracing are critical, those conditions can allow chains of transmission to spread before they are detected.

Health officials are now trying to scale up a response to match that threat. On June 5, WHO and Africa CDC launched a joint continental preparedness and response plan seeking $518 million for June through November 2026. WHO’s latest risk assessment rates the outbreak as very high nationally in DRC, high at the regional level and low globally. A CDC modeling analysis published in June found the outbreak could grow to thousands of cases within three months if people with symptoms are not isolated quickly enough.

The latest figures are significantly higher than those cited in some earlier assessments because the outbreak picture changed quickly as testing caught up. On June 3, WHO Director-General Tedros Adhanom Ghebreyesus said, “In DRC, 344 cases have been confirmed, including 60 deaths.” He also said Uganda had 15 confirmed cases and one death. Those numbers matched the WHO snapshot reflected in a Lancet comment published around that time. WHO later revised the totals upward after backlogged samples were processed, giving a fuller picture of an outbreak that is spreading in one of the hardest places in the region to contain it.