Dozens of workers at an Ebola treatment center in northeastern Democratic Republic of Congo launched a strike on Monday, protesting unpaid salaries and bonuses, adding fresh pressure to the country's rapidly expanding Ebola outbreak.

The strike comes as Congo continues to battle an outbreak of the rare Bundibugyo strain of the Ebola virus, which has no approved vaccine or treatment. Health authorities confirmed last week that the outbreak has spread to two additional provinces.

The protesting workers at Rwampara General Hospital in Ituri province—the epicenter of the outbreak—include epidemiologists, case investigators, drivers and gravediggers. They accuse authorities of failing to pay them for the past two months.

The demonstrators shut down the treatment center, blocked access roads and burned tires outside the facility in protest.

"We don't know how it is possible to go unpaid for two months," one health worker said, adding that despite the protest, they do not want to abandon their work.

The Rwampara facility is separate from another treatment center in Ituri where clinical trials of two experimental Ebola treatments began earlier this month.

Congolese authorities officially declared the outbreak on May 15 after the virus had spread undetected for several weeks. According to the World Health Organization (WHO), the delay in confirming the outbreak was partly due to initial testing for a more common Ebola strain. 

During a recent visit to Ituri, Health Minister Roger Kamba said the government was reviewing payroll records after discovering that names of individuals not involved in the response had been added to payment lists.

He said the verification process aims to ensure that frontline workers receive their due compensation while addressing complaints from those who have not been paid.

According to Congolese health authorities, the outbreak has so far resulted in 1,926 confirmed cases, including 702 deaths.

Meanwhile, WHO Director-General Tedros Adhanom Ghebreyesus said a second American humanitarian worker infected with Ebola in eastern Congo had been transferred to Germany for treatment. The first infected American was a doctor working in Congo during the early stages of the outbreak.