Health authorities reported 550 confirmed cases as of Sunday, including 101 deaths and 19 recoveries, according to the latest situation update released late Monday. The outbreak was officially declared on May 15.

The vast majority of infections have been recorded in Ituri province, which accounts for more than 90 percent of confirmed cases. Additional cases have been identified in North Kivu and South Kivu provinces, while the virus has also crossed into neighboring Uganda.

Officials believe the true number of infections may be higher because the outbreak was detected weeks after transmission had already begun. Response efforts have been further complicated by the absence of an approved vaccine or treatment for the strain responsible for the current outbreak.

The outbreak has been linked to the rare Bundibugyo strain of Ebola virus, for which no approved vaccine or therapeutic treatment currently exists. This differs from the Zaire strain, which was responsible for most of Congo’s previous Ebola outbreaks and for which vaccines and treatments have been developed.

Authorities said the sharp increase in confirmed infections partly reflects expanded diagnostic capacity, which has enabled laboratories to process a backlog of previously collected samples.

Health workers operating in affected areas continue to face significant obstacles. Medical teams have been attacked on multiple occasions by residents frustrated by the outbreak response, while persistent skepticism among some communities has complicated surveillance and containment efforts.

Security concerns remain a major challenge across eastern Congo, where numerous armed groups continue to operate. Ongoing violence has limited access to several affected communities and disrupted disease-monitoring activities.

The World Health Organization said Monday that insecurity is restricting access for response teams, hindering surveillance operations and increasing the risk that new chains of transmission could go undetected.

The agency said the attacks on health personnel underscore the difficulties of responding to a public health emergency in conflict-affected areas and highlighted the importance of cooperation with local leaders and communities.

Eastern Congo has experienced repeated outbreaks of Ebola over the past decade, but health officials warn that the combination of armed conflict, delayed detection and the lack of approved medical countermeasures for the Bundibugyo strain presents a particularly complex challenge for containment efforts.