The World Health Organization has declared the Ebola outbreak linked to the Bundibugyo virus strain in the Democratic Republic of Congo and Uganda a public health emergency of international concern, warning of rising cross-border transmission risks and major gaps in containment.

The Bundibugyo strain of Ebola was first identified in Uganda in 2007 and is one of several Ebola virus species known to cause severe hemorrhagic fever in humans. Unlike the Zaire ebolavirus species, for which vaccines and treatments are available, there are currently no licensed vaccines or targeted therapeutics for the Bundibugyo virus, according to the WHO.

In a statement issued on Sunday, WHO Director-General Tedros Adhanom Ghebreyesus described the outbreak as "an extraordinary event" requiring urgent international coordination because of its rapid spread, insecurity in affected regions and the absence of approved medical countermeasures specifically targeting the strain.

"The high positivity rate of the initial samples collected, the confirmation of cases in both Kampala and Kinshasa, the increasing trends in syndromic reporting of suspected cases and clusters of deaths across the province of Ituri all point toward a potentially much larger outbreak than what is currently being detected and reported," the WHO said.

As of Saturday, health authorities had reported eight laboratory-confirmed Ebola cases, 246 suspected infections and 80 suspected deaths in Ituri Province in eastern DR Congo, concentrated in the Bunia and Mongbwalu health zones. A confirmed case was also detected in Kinshasa involving a traveler returning from Ituri.

Uganda has separately confirmed two Ebola cases in Kampala within 24 hours, including one death, both linked to travelers arriving from the DR Congo. The WHO said the two cases appeared unrelated, raising fears of undetected transmission chains. Both patients were admitted to intensive care units in Kampala.

Health officials have also reported unusual clusters of community deaths with symptoms consistent with the Bundibugyo virus strain in several areas of Ituri and neighboring North Kivu Province.

At least four healthcare workers have died in circumstances suggestive of viral hemorrhagic fever, increasing concerns that infections may be spreading inside health facilities amid weak infection prevention and control measures.

The WHO said international coordination would now be critical to strengthen surveillance, improve infection prevention, scale up emergency operations and prevent wider regional spread.