The ongoing Ebola outbreak in Democratic Republic of Congo concerns a previously unseen variant of the rare Bundibugyo species of the virus, indicating it stemmed from a new transmission from animals to humans rather than from variants linked to earlier outbreaks, a new study said.

Researchers from Congo, Uganda, Belgium and other countries analysed the genetic make-up of virus samples from 22 patients in Congo and Uganda and found the outbreak strain was genetically distinct from previous Bundibugyo Ebola viruses seen in outbreaks in 2007 and 2012.

The findings, published on Monday in the journal Nature Medicine, suggest the outbreak began with a fresh animal-to-human transmission event and was then spread between people.

The study did not identify the animal source of the outbreak, but Ebola viruses are known to spill over periodically from infected animals to humans.

The genetic analysis helped confirm that cases detected in Uganda were linked to the outbreak in Congo.

The study's authors said wider access to testing and virus sequencing could help detect future Ebola outbreaks earlier and improve efforts to contain them.

There is no approved vaccine or treatment for Bundibugyo, although candidate vaccines and treatments are under development.

The outbreak was declared on May 15 and has surpassed 2 000 deaths, with 4 381 confirmed cases so far, according to the latest government data.