A rare Ebola outbreak that may have circulated undetected in northeastern Democratic Republic of Congo for several weeks has exposed the difficulty of detecting deadly viruses in regions where malaria, typhoid and other fever-causing illnesses were common and health systems were stretched thin.

About 350 suspected cases and 91 deaths have been reported in northeastern DR Congo, the country’s health minister Roger Kamba said on Sunday, while neighbouring Uganda has confirmed two infections, including one death in Kampala.

A separate case was also reported Sunday in Goma, the eastern Congolese city controlled by Rwanda-backed M23 rebels.

“Hospitals are already under pressure,” Kamba told reporters in Bunia, the capital of Ituri province, where the outbreak is believed to have begun in April and hospitalised 59 people. “It’s not a mystical illness,” he said, urging people with symptoms to seek treatment quickly to help slow transmission.

The outbreak is caused by the Bundibugyo strain of Ebola virus. DR Congo’s presumed first patient, a nurse in Bunia, developed symptoms on April 24, according to Jean Kaseya, director general of the Africa Centres for Disease Control and Prevention.

By the time health authorities were first alerted to the outbreak on social media on May 5, 50 deaths had already been recorded, the Africa CDC said.