The Ebola outbreak in eastern Democratic Republic of Congo is probably two to four times larger than the 1,960 confirmed cases and more than 700 deaths officially recorded, the World Health Organization said on Tuesday. Chikwe Ihekweazu, WHO emergencies director, told reporters in Geneva that modelling indicated the epidemic’s scale was “at least two to four times the number of cases that we have found”. The outbreak, caused by the rare Bundibugyo species for which no approved vaccine or treatment exists, has already become the third-largest ever recorded and is now spreading faster in a single month than any previous Ebola epidemic, he added.

That assessment is driven partly by the high proportion of new cases with no known epidemiological link: around four in five infections are detected in people not listed as contacts of existing patients. Many of the newly reported cases are individuals who died in their communities without ever reaching a health facility, Ihekweazu noted. While contact-tracing rates have improved to nearly 80 per cent and treatment capacity has expanded to more than 700 beds, the virus continues to outpace response efforts across five affected provinces — Ituri, North Kivu, South Kivu, Tshopo and Haut-Uele — and has spilled into neighbouring Uganda, which has recorded 20 cases.

At the outbreak’s epicentre in Ituri province, dozens of health workers at the Rwampara treatment centre burned tyres and blocked access on Monday, protesting that they have not been paid since the epidemic was declared on 15 May. Staff, including epidemiologists, drivers and gravediggers, issued a 48-hour ultimatum for salaries and bonuses, threatening a full-scale strike with no minimum service. Health Minister Samuel Roger Kamba, visiting Ituri last week, acknowledged “delays in payment” and promised to resolve what he called an organisational issue. A prolonged walkout would severely disrupt case detection, safe burials and the clinical trial of two experimental therapies — Gilead’s remdesivir and Mapp Biopharmaceutical’s MBP134 — that began enrolling patients this month at a single treatment centre in Ituri. Researchers caution that it could take months and up to 1,000 participants to determine whether either drug is effective.

International donors have pledged $1.5 billion for the response, yet the WHO says it has received only 40 per cent of the $115 million it requires for its own emergency operations. The funding gap, combined with the strike threat and the difficulty of tracing cases in a region scarred by three decades of armed conflict and mass displacement, leaves the containment effort finely balanced. The next milestones will be whether the Congolese government meets the health workers’ pay demands before the ultimatum expires, and whether the treatment trial can safely expand to additional sites.