New genomic research published in the medical journal Nature Medicine indicates that the Ebola outbreak now ravaging eastern Democratic Republic of the Congo (DRC) began with a fresh transmission of the virus from animals to humans, rather than from variants linked to earlier outbreaks.
Scientists from the DRC, Uganda, Belgium and other countries analyzed genetic material from 22 patients in the DRC and Uganda and found the outbreak strain is genetically distinct from the Bundibugyo Ebola viruses responsible for outbreaks in 2007 and 2012. They concluded the current outbreak originated in a new animal-to-human spillover event, which then spread among people. The animal source has not been identified, but researchers said the outbreak in Uganda was linked to the one in the DRC.
The outbreak, formally declared on May 15, has killed more than 2,000 people among 4,449 recorded cases, making it the fastest-moving Ebola outbreak on record. Genetic sequencing later showed the virus had actually been circulating since February. The World Health Organization (WHO) said on Wednesday that the Bundibugyo strain is spreading faster than health authorities can contain it and is on track to become the deadliest outbreak on record, potentially eclipsing the 2014–2016 West African crisis that killed at least 11,300 people.
Infectious disease experts caution that the finding does not mean a new form of Ebola has emerged or that animals are transmitting the virus differently. Krutika Kuppalli, an infectious diseases doctor with experience in Ebola response, explained that the genomic data simply suggest the current outbreak began with a new zoonotic spillover — the virus crossed independently from an animal reservoir into a person — rather than re-emerging from a previous human outbreak. After that initial spillover, human-to-human transmission has driven the outbreak.
The Bundibugyo strain currently lacks the licensed, virus-specific treatments available for the Zaire ebolavirus, making supportive care — including aggressive fluid and electrolyte management, treatment of shock and organ dysfunction, and management of co-infections — critical while investigational therapeutics are evaluated.
Kaja Abbas, an associate professor of infectious disease epidemiology at the London School of Hygiene & Tropical Medicine and Nagasaki University, said the human-to-human transmission dynamics of the Bundibugyo virus are what make it dangerous, not the initial animal origin. Researchers behind the study called for expanding decentralized laboratory diagnostic capacity, including genomic sequencing and timely detection, to pre-empt future outbreaks. Experimental vaccines and treatments targeting the current Bundibugyo strains are in the clinical development pipeline, and the WHO has dispatched 12 tonnes of medical supplies, including personal protective equipment, to the DRC.