(AP) – The Ebola outbreak in eastern Congo is now the fastest-growing one in history with just under 1,000 people dead, and new challenges are emerging in containing a type of the virus with no approved treatment or vaccine.

Strikes by unpaid workers at health centers at the heart of the outbreak could light the flame for others in a remote region already suffering from bare-bones infrastructure, rebel threats and misinformation asserting that the deadly virus isn’t real.

The latest update from Congo’s health ministry shows that as of Monday, 2,473 cases have been confirmed and 999 people have died. The outbreak is mostly concentrated in Ituri province, which accounts for nearly 90% of cases.

Cases have been confirmed in five provinces, including one of Congo’s largest cities, Kisangani, as responders struggle to understand how far Ebola has spread. The vast majority of new cases are emerging from unknown chains of transmission, the World Health Organization has said. The outbreak’s origin is still not known.

Here’s a look at the outbreak and the growing effort to contain it.

This type of Ebola is rare
The Ebola outbreak is caused by the rare Bundibugyo virus, which contributed to a costly delay in confirming the outbreak as lab tests were performed for the more common type instead.

Ebola is highly contagious and spreads in the human population through contact with bodily fluids such as vomit, blood or semen, and with contaminated surfaces and materials such as bedding and clothing.

Traditional funerals in which loved ones wash and prepare bodies have been restricted, which has angered some residents.

The disease is rare but severe and often fatal. Symptoms include fever, vomiting, diarrhea, muscle pain and at times internal and external bleeding. Outbreaks often occur in remote villages in Central Africa, near rainforests.

This outbreak is occurring in a volatile, violent region
Associated Press journalists have witnessed the aftermath of attacks on health centers by a wary, highly mobile population that has long been traumatized by armed groups.

Outsiders can be looked upon with suspicion, and community outreach teams have worked to spread the word about Ebola prevention measures in the face of abuse and accusations that the outbreak is a scam.

Part of the outbreak is unfolding in a major city and humanitarian hub, Goma, that rebels backed by neighboring Rwanda seized over a year ago, further complicating the response.

Now there is unrest among local Ebola responders themselves after weeks of risky crisis work and little or no pay from the Congolese government. Some staff have gone on strike at treatment centers and blocked access. Striking staffers included epidemiologists, case investigators, drivers and gravediggers. Some later agreed to resume work under the condition that the government pays them soon.

A labor strike that spreads to more overstretched and underequipped facilities would be another serious blow to Ebola containment efforts. Congolese officials have said they are in talks to find a solution.

The first participants are enrolled in a treatment study
The strikes come at a vulnerable time. Researchers have begun a study of two possible Ebola treatments, enrolling local participants at an Ebola treatment center in Ituri province.

One is Gilead Sciences’ remdesivir, a broad-acting antiviral approved to treat COVID-19 that has shown some hints in lab tests that it may help fight the Bundibugyo virus. The other is Mapp Biopharmaceutical’s experimental MBP134, antibodies engineered to target Ebola viruses, including Bundibugyo.

The WHO has said patients will be randomly assigned to receive today’s best standard of care as well as remdesivir, MBP134, both or neither.

The United Nations body has warned it could take months and possibly as many as 1,000 study participants to tell if either drug works.