The World Health Organization warned Wednesday that an Ebola outbreak in the Democratic Republic of Congo was expanding faster than any previously recorded. The alert came days after a US humanitarian worker tested positive for the virus.

Congolese health authorities and the WHO have tracked a growing cluster of confirmed infections in recent weeks. The infection of the American aid worker, first reported July 14, drew international attention and prompted the US Centers for Disease Control and Prevention to review evacuation and treatment options.

The WHO said it was deploying additional field teams and shipping doses of the Ervebo vaccine, produced by Merck, to support ring vaccination of contacts and frontline health workers. A WHO spokesperson said case-fatality rates remained a serious concern given delays in isolating early patients.

Health ministries in neighbouring countries, including Uganda and Rwanda, were advised to strengthen border screening and case-finding. Aid organisations operating in the region, including Doctors Without Borders, warned that insecurity and limited health infrastructure could hamper containment efforts.

The outbreak revived memories of Congo's 2018-2020 eastern epidemic, which killed more than 2,000 people. WHO officials said the current spread underscored the need for sustained funding for outbreak preparedness across central Africa.