Fastest-growing Ebola outbreak in history has claimed 2,000 lives. Here's why it is hard to contain

More than 2,000 people have now died in the fastest-growing Ebola outbreak in history, and challenges keep coming in containing a rare type of the virus with no approved treatment or vaccine.

Congo's health authorities on Tuesday announced 4,381 confirmed cases, including 2,011 deaths. This death toll has been reached almost three times faster than in the 2014-16 Ebola outbreak in West Africa — the worst in history.

The outbreak is unfolding in some of the most challenging conditions imaginable, with strikes by some unpaid health workers, threats by rebel groups, anger from long-traumatized communities and misinformation asserting that Ebola isn't real. Health teams travel remote, unpaved roads and have reported shortages of protective gear, while a vast population of displaced people struggles to find reliable water sources for washing hands.

Five provinces in eastern Congo are affected, near neighboring South Sudan, Uganda and Rwanda, and there are fears about the potential spread to larger cities in the region with a highly mobile population and many people fleeing conflict.

On Monday, the World Health Organization said the outbreak started in February, months before it was officially declared in mid-May, as experts try to track down how it began. Health authorities have said between 60% and 70% of new cases are recorded outside contacts being monitored, and that the disease is spreading at an "alarming" rate.

"We are chasing the virus, the virus is ahead of us," the WHO regional director for Africa, Dr. Mohamed Yakub Janabi, said this week.

Here's a look at the outbreak and the challenges to contain it.

This is a rare type of Ebola

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 and contributed to the hostility that some health workers have faced.

READ MORE: Congo's fast-moving Ebola outbreak started month before it was declared, WHO says

Ebola 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 is the 17th known Ebola outbreak in Congo, and experts have said the country is well-placed to apply lessons learned.

But the shortage of supplies like protective gear is just one challenge.

The 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.

Health teams travel under the threat of attack by armed groups. 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.

This outbreak is deadly because of limited care

Ebola can be caused by different types of virus. Although the type responsible for the 2014-2016 outbreak is considered the deadliest, government data shows this Bundibugyo outbreak has killed a higher percentage of people as care and support are not getting to patients quickly enough.

Access to healthcare in the region already had been challenged by years of rebel conflict in one of Congo's most remote and vulnerable areas. Now some pregnant women and others are avoiding health centers for fear of the virus, at risk to their lives.

After weeks of risky crisis work and little or no pay from the Congolese government, some local Ebola responders have gone on strike at treatment centers and blocked access. Striking staffers included public health researchers, case investigators, drivers and gravediggers. Some later agreed to resume work on condition that the government pays them soon.

A labor strike that spreads to more overstretched, underequipped facilities would be another serious blow to Ebola containment efforts.

The first participants have been enrolled in a treatment study

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.

Associated Press writers Mike Stobbe in New York and Naa Adorkor Cudjoe in Accra, Ghana, contributed.