The agency said insecurity, population movement and operational constraints were complicating surveillance and contact tracing efforts, particularly in eastern DRC, where most cases have been reported.
The World Health Organisation (WHO) has raised concerns over mounting challenges in containing the Ebola outbreak caused by the Bundibugyo virus in the Democratic Republic of the Congo (DRC) and Uganda.
In its latest situation report, the global health body said 528 suspected cases and 132 deaths had been reported across both countries as of 18 May.
The agency said insecurity, population movements, and operational constraints were complicating surveillance and contact-tracing efforts, particularly in eastern DRC, where most cases have been reported.
It also noted that the outbreak figures remain fluid as investigations, laboratory testing and active surveillance continue to expand.
“Numbers are rapidly changing as surveillance, contact tracing, and laboratory testing are being scaled up,” the report stated.
The latest figures represent a rise from the 246 suspected cases and 80 deaths earlier reported in Ituri Province, eastern DRC, when the outbreak was officially declared earlier this month.
The outbreak, linked to the rare Bundibugyo strain of Ebola, was first detected in Ituri Province near the borders with Uganda and South Sudan.
According to the WHO and Africa CDC reports, the virus circulated for weeks before laboratory confirmation, allowing infections to spread across communities and borders.
The Africa CDC had earlier warned that the outbreak began in Mongbwalu, a mining town with high population movement, before infected persons travelled elsewhere in search of treatment.
WHO also acknowledged major uncertainties surrounding the true scale of infections.
“There are significant uncertainties to the true number of infected persons and geographic spread associated with this event at the present time,” WHO stated.
The outbreak has since spread into Uganda, where authorities confirmed two Ebola infections in Kampala linked to travel from DRC.
According to the latest report, Uganda has recorded 12 suspected Ebola cases linked to the outbreak, but laboratory testing confirmed only two infections, while the remaining suspected cases tested negative.
Across both countries, health authorities have identified 668 contacts linked to suspected infections, including 541 in DRC and 127 in Uganda.
However, the WHO warned that tracking exposed persons remains difficult in several Congolese communities affected by insecurity and movement restrictions.
“Contact follow-up remains challenging in some areas of DRC due to insecurity and movement restrictions,” the report read.
The WHO declared the outbreak a Public Health Emergency of International Concern (PHEIC), its highest level of global alert under the International Health Regulations.
The agency warned that regional spread remains a major concern due to porous borders, trade routes, and population mobility across Central and East Africa.
The WHO Director-General, Tedros Ghebreyesus, said neighbouring countries remain vulnerable to further transmission due to ongoing travel and epidemiological uncertainty.
Despite the emergency declaration, the WHO advised countries against imposing border closures or travel bans, warning that such restrictions could push travellers towards informal crossings and undermine surveillance efforts.
To strengthen outbreak control efforts, the WHO said alert management and case investigations are being scaled up in both affected countries as authorities attempt to contain transmission.
In the DRC, 38 experts, including 20 officials from the Ministry of Health and 18 WHO personnel, were deployed from Kinshasa to Bunia to support outbreak response activities.
The agency also said more than 17 tonnes of emergency supplies had been delivered to the DRC. The supplies include personal protective equipment, medicines, tents, stretchers and other medical materials.
“Laboratory capacity is being expanded, with deployment of lab teams and mobile laboratories to affected areas in DRC to increase local testing and diagnostic activities,” the WHO said.
The WHO said it is working with humanitarian and medical partners, including the Alliance for International Medical Action, Médecins Sans Frontières, the International Organisation for Migration, and the International Federation of Red Cross and Red Crescent Societies, to set up treatment facilities in affected areas.
The agency added that risk communication and community engagement were also being scaled up to improve public participation in the response.
The Bundibugyo virus is a Risk Group 4 pathogen and one of the less common Ebola virus strains. Unlike the Zaire strain, which has approved vaccines, there is currently no licensed vaccine specifically targeting the Bundibugyo variant.
