A mobile lab sits in front of the National Center for Blood Transfusion in Conakry, Guinea on Jan. 28. (Jane Hahn/For The Washington Post)

The race to find a cure for Ebola is heating up, with scientists launching experiments in West Africa that are among the most ambitious ever aimed at taming the devastating disease.

But they are encountering an unexpected challenge: finding enough Ebola patients as the outbreak recedes.

In Liberia, researchers had to scrap a clinical drug trial at the end of January because of a lack of Ebola patients. Another trial there, using donations of blood plasma, has struggled to enroll enough participants. Its organizers may be forced to move it to Sierra Leone.

Guinea offers a glimpse of the promise and difficulties of the new experiments. This month, officials said a small trial of a Japanese antiviral drug in Guinea’s forest region had yielded encouraging early results. The government announced Saturday that the drug may be distributed in additional areas.

On Monday, a Belgian-led team in Guinea launched a highly anticipated experiment testing whether the blood plasma of Ebola survivors can save lives. Another trial is expected to begin within weeks to test two vaccines. But both experiments need scores of patients with the virus in order to produce statistically significant results.

How trials will work for Ebola vaccines

New Ebola cases in Guinea have fallen to only about 40 per week, compared with more than 100 near the end of last year, according to the World Health Organization. Neighboring Liberia recently had five new cases, while Sierra Leone had about 80.

There is no cure or proven vaccine for Ebola. In the current outbreak, roughly 60 percent of people infected by the virus have perished, amounting to a death toll of more than 9,000 people.

Scientists had always expected to encounter complications in carrying out their experiments in West African countries with widespread distrust of modern medicine. But now they are also concerned about finding enough Ebola patients to meet a scientific burden of proof.

“There are so few patients, and time is moving quickly,” said Christine Danel, a physician leading the antiviral drug trial.

Plasma holds promise

A bright blue bus is parked near the Donka Hospital in Conakry, the Guinean capital. The bus houses a mobile laboratory and a hefty piece of equipment that is the Cadillac of plasmapheresis, a process that separates the yellowish plasma from the rest of the blood. On Monday, a trial began here to find out whether disease-fighting antibodies in the plasma of Ebola survivors can help cure current patients.

This approach was first tried in 1995 in Congo — then known as Zaire — when eight patients were given whole-blood transfusions from survivors. Seven survived. Since then, there have been anecdotal stories of other successes, most recently when U.S. physician Kent Brantly, an Ebola survivor, donated his plasma to several patients.

The experiment in Conakry, funded by the European Union and the Bill & Melinda Gates Foundation, aims to test 130 patients over a nine-month period.

A member of the cleaning team scrubs the decontamination zone at the Alliance for International Medical Action Ebola Treatment Unit in Nzerekore, Guinea on Jan. 24. (Jane Hahn/for The Washington Post)

“I think there is a good chance that it will work, but of course, you have to prove it scientifically,” said Sarah Temmerman, a doctor working with the Belgium-based Institute of Tropical Medicine, which is leading the team working on the trial.

The team had hoped to begin in December. But researchers first had to present the experiment to several ethical-review boards, then train local staff members to operate the plasma machine and store plasma. Most importantly, they had to find Ebola survivors willing to provide blood.

In Guinea, donating blood is not a common practice. Some people have been misled by rumors that giving blood could weaken them or that receiving it could harm them.

Bakary Oularé, 30, a physician who heads a club of more than 200 Ebola survivors in the Conakry area, said he would give blood in order to set an example for others.

“If they see me as a doctor donating my blood, they will have confidence for themselves,” he said.

But even if there are enough donors, there may be too few Ebola victims available or willing to receive the plasma.

“Everyone is really curious to see: Will it work? And is this an option? Of course, you need patients for that,” said Roeland Scholtalbers, the spokesman for the Institute of Tropical Medicine. “If the epidemic is over, of course we’re all very happy that it is, but for science, it is of course important to know that this [treatment] has potential.”

Results said to be ‘encouraging’

The experiment that has generated the highest expectations so far involves a Japanese antiviral drug called favipiravir. In December, the French National Institute of Health and Medical Research, known as Inserm, began testing the drug at two Ebola treatment centers in the cities of Nzerekore and Gueckedou in Guinea’s forest region.

Some have compared the pill to Tamiflu, a popular flu medication that is most effective when used soon after symptoms emerge. Favipiravir, which is made by Toyama Chemical, works by changing the way that the Ebola virus replicates.

Researchers set out to test 60 patients within 48 hours of their showing symptoms, said Danel, who works for Inserm.

The French institute has not released its findings. But French President François Hollande’s office said that the results had been “encouraging.” Last week, the New York Times reported that a draft copy of early results showed the drug had halved mortality rates “in patients with low to moderate levels of Ebola in their blood.” The pill had been tested on nearly 70 patients, although most of them did not seek care until about five days after their symptoms appeared, according to the report.

A spokeswoman for Inserm, Priscille Rivière, declined to confirm the report but said that “encouraging data” will soon be made public.

Sakoba Keita, coordinator for Guinea’s Ebola response, told reporters in Conakry on Saturday that “we have decided to broaden the use of this drug,” according to the Reuters news agency. He said that it would be provided to patients in the town of Coyah and that discussions were underway to distribute the pill in Conakry.

Susan Shepherd, a U.S. pediatrician, recently worked at the Alliance for International Medical Action clinic in Nzerekore, where the drug was tested. She said that around Christmas, about two dozen patients there had begun treatment. By New Year’s Day, many of them were shouting for newspapers and asking for radios so they could dance to music, she said. But she cautioned that “for patients who arrive with a very high viral load, it does not make a difference.”

More trials on horizon

Meanwhile, a test of two experimental Ebola vaccines began recently in Liberia, and trials in Guinea and Sierra Leone are expected to start this month. The development of vaccines normally takes years, but the process was fast-tracked as the epidemic raged.

In Guinea, the trials will use the “ring” approach, which led to the eradication of smallpox in 1980.

Scientists running the randomized trial will identify Ebola patients and then vaccinate a circle of people closest to them — family members, neighbors, co-workers. Some “rings” of people will be vaccinated immediately, and those results will be compared against “rings” of people vaccinated a few weeks later.

Daniela Bagozzi, a spokesman for the WHO, said the organizers are aiming to vaccinate human “rings” around 190 Ebola patients.

But their success will depend on the course of the virus.

If the number of Ebola cases holds steady or increases, the WHO believes the study could be completed in six to eight weeks. But if cases sharply decrease, the outcome of the trial could be in question.