Unprecedented trials on patients in west Africa to test Ebola drugs are all set begin under the aegis of global aid agency Doctors Without Borders.
The trials in Guinea are aimed at rushing out an emergency therapy to battle an epidemic which has taken more than 5,000 lives since December.
"This is an unprecedented international partnership which represents hope for patients to finally get a real treatment against a disease that today kills between 50 and 80 percent of those infected," said Annick Antierens, who is coordinating the trials for the medical charity, known by its French initials MSF.
The first trials are due to start in December and results could be available by February next year, MSF said.
Ebola, transmitted through bodily fluids, leads to haemorrhagic fever and -- in an estimated 70 percent of cases in the current outbreak -- death.
There is no specific treatment regime and, as yet, no licensed vaccine -- although one of the leading candidates, known as ChAd3 and made by Britain's GlaxoSmithKline, is being tested in Mali and elsewhere.
Patients' best chance of survival, if their condition is caught early enough, is taking paracetamol for their fever, rehydrating and being kept well nourished.
- 'Miracle drug' -
The French National Institute of Health and Medical Research (INSERM) will trial antiviral drug favipiravir in Gueckedou, southern Guinea.
Meanwhile, the Antwerp-based Institute of Tropical Medicine (ITM) will lead trials of "convalescent whole blood and plasma therapy" at MSF's Donka Ebola centre in Conakry, Guinea's capital.
MSF is in discussion for a third trial, on antiviral brincidofovir, in Liberian capital Monrovia but has not yet been given the green light.
The drugs have been shown to work on other viruses, but not Ebola, Antierens told AFP.
"Either it is very efficient, and then it is a miracle drug... (or) it is not efficient at all, and this is very much possible. We have reason to believe that that is not the case, but it is still very much possible," she added.
She added that there could be "an intermediary result, whereby it's promising and we're not sure if it will be efficient for every patient".
Ebola, which emerged in Democratic Republic of Congo in 1976, is one of the most aggressive pathogens known to humankind, and victims tend to die a few days after showing symptoms.
The target for a successful trial in each of the treatments under consideration will be the patient surviving for two weeks, said MSF, adding that no one would be tested without informed consent.
The charity said there would be little disruption to the patients' normal care.
Patients in the Conakry trial will be administered with blood or plasma containing antibodies from survivors.
- 'New experience' -
Lead coordinator Johan van Griensven called on recovered patients to give blood, saying their help in coming up with a treatment could reduce the stigma they encounter back in their villages.
"We want to find out whether it works for Ebola, whether it is safe and whether it can be scaled up to reduce the number of deaths in the current outbreak," he said.
The antivirals were selected from a shortlist drawn up by the World Health Organization (WHO), which is overseeing the project, after a review of a wide range of issues, including trials on non-human primates and availability.
"Conducting clinical trials of investigational drugs in the midst of a humanitarian crisis is a new experience for all of us, but we are determined not to fail the people of west Africa," said Peter Horby, who is expected to lead the Monrovia trial if it gets the go-ahead.
The trials will be the first ever on Ebola patients, Horby told AFP.
"Every time a patient gets to day 14, we will recalculate the numbers and see what proportion of patients are alive or dead... So once we have confidence that the fatality rate is 50 percent or worse, then we would say there is no evidence that the drug is improving things, because that's about the rate we see, and then we would stop the trial," he added.
"If the survival rate is 80 percent or better, we would say that this is good evidence that the trial is effective."
Almost all of the deaths in the current outbreak have been in Liberia, Sierra Leone and Guinea, but smaller outbreaks have emerged in Nigeria, Senegal, the United States and Spain.
Mali is scrambling to prevent a serious epidemic after the deaths of an Islamic cleric in October and, this week, the nurse who treated him in the capital Bamako.
The WHO announced on Wednesday that the outbreak had passed a gruesome landmark, with 5,160 deaths from around 14,000 cases since Ebola emerged in the forests of southern Guinea.