Deaths from Ebola in the Congo have passed 1,000, according to world health officials who see no quick end to the nine-month-old epidemic.

The World Health Organization (WHO) said it expected the infection to continue spreading though the east of Democratic Republic of Congo.

In an effort to control the “intense transmission” of the second-worst epidemic of the virus on record, the U.N. health agency has begun the first-ever trial to test the effectiveness and safety of four experimental Ebola drugs. It’s the first time scientists have directly compared such treatments, the WHO said.

Enrolled patients will receive one of the four trial therapies, as well as standard, supportive care including fluids, electrolytes and painkillers.

“While our focus remains on bringing this outbreak to an end, the launch of the randomized control trial in DRC [Congo] is an important step toward finally finding an Ebola treatment that will save lives,” said WHO Director-General Tedros Adhanom Ghebreyesus.

The four therapeutic drugs being used to treat patients are mAb 114, ZMapp, Remdesivir and Regeneron, according to Congo’s Health Ministry.

To date, more than 160 people have been treated with these experimental drugs. The number of patients who participate “will depend on the evolution of the epidemic and the willingness of patients to participate,” the Congolese health ministry said.

Researchers will compare death rates between each group of enrolled patients after 28 days of treatment to determine each drug’s effectiveness. All four treatments on trial have been studied in animals. The three antibody treatments have been deemed safe for human use, while safety testing of the antiviral in people is underway.

With the trial data, “we’ll be able to say, ideally, that this drug or that drug actually does work, not just we think or hope it does work,” says Richard Davey, one of the principal trial investigators and the deputy clinical director at the U.S. National Institute of Allergy and Infectious Diseases in Bethesda, Md.

Congo, with poor infrastructure, presents a difficult environment for administering these treatments. ZMapp is difficult to use; it takes three infusions, given over hours. If patients are treated with Remdesivir, their liver function must be analyzed regularly.

Infectious disease epidemiologist Mosoka Fallah of the National Public Health Institute of Liberia called the availability of vaccines “the one silver lining in the entire dark cloud.” The deployment of the vaccine and the treatments have kept the outbreak from becoming far worse than it already is, he said.

“As much as it is a bleak situation, it is hopeful,” Fallah said.