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As west Africa struggles to contain the biggest ever outbreak of Ebola, some experts say an unusual but simple treatment may help: the blood of survivors.
The evidence is mixed for using infection-fighting antibodies from survivors' blood for Ebola, but without any approved drugs or vaccines for the deadly disease, some say it's worth trying.
"This is something that's fairly simple to do," said Dr Peter Piot, director of London's School of Hygiene and Tropical Medicine and co-discoverer of the Ebola virus.
Using the blood of survivors is one of the experimental Ebola treatments under discussion at a two-day meeting that began on Thursday in Geneva. More than 200 experts assembled by the World Health Organisation are looking at issues of safety and effectiveness and considering which treatments should be prioritised for testing.
Several medicines and vaccines are in development. None has been tested in humans but an early trial of one vaccine began this week in the US.
Much attention has focused on the unproven drug ZMapp, which was given to seven patients, two of whom died. But the limited supply is now exhausted and its developer says it will take months to make even a modest amount.
In contrast, WHO's blood network, an international group of blood regulators, noted recently there are thousands of survivors from past Ebola outbreaks in Africa who could be a source of the experimental treatment.
In another document published this week, WHO estimated the first batches of survivors' blood could be available later this year. The agency said it had identified several recovered patients as potential donors, but acknowledged "logistics of blood collection are an issue". Some scientists think antibodies in the blood of Ebola survivors could help patients infected with the deadly disease.
Antibodies are produced by the body's immune system to fight off harmful things such as viruses. They remain in the blood ready to fight off any future infections by the same foreign substance.
Piot said it was vital to find out if the blood treatment was effective. "I hope this is the last Ebola outbreak where all we have is isolation, quarantine and supportive care to treat patients," he said.
Experts say blood from survivors could be collected and processed for multiple patients, or a survivor could donate blood to an individual patient. Both methods require screening blood for diseases such as HIV or malaria.
While direct donation would be easier, the levels of Ebola-fighting antibodies produced by a survivor can vary. Ideally, experts said, the amount of antibodies should be measured.
"With drugs, you can at least do some quality control," said Tom Geisbert, an Ebola expert at the University of Texas medical branch at Galveston. "If you're just taking blood blindly from [survivors] without testing it for antibody levels, how can we predict what outcome they will have?" he said.
In west Africa, there have been no organised attempts to use the blood of survivors to treat patients. Blood from a 14-year-old boy who survived Ebola was given in July to the American doctor Kent Brantly, who was infected in Liberia. Brantly also got some ZMapp and was released from an Atlanta hospital last month. It's unknown whether the drug or the boy's blood aided his recovery.
Blood from survivors of diseases including Ebola, bird flu and anthrax has been used in the past when doctors ran out of options and seems to work best in diseases where there's a toxin, such as anthrax and tetanus.
For treating Ebola, "you would need to come up with how much you should give, how long, and what's a safe infusion rate," said Dr Michael Kurilla, director of BioDefense at the US National Institutes of Health. "If you know what the potency of the serum is, you could theoretically help the body clear Ebola out of their cells before it can do too much damage."
Dr Colin Brown, who recently worked in Ebola clinics in Sierra Leone for King's College London's partnership with the country, said local hospitals should be able to provide survivors' blood if doctors wanted to offer it.
So far, more than 3,000 people have been infected. Last week, WHO estimated there could be another 20,000 cases before the Ebola outbreak is stopped, a figure Brown described as unfortunate but realistic.
"It does give us the opportunity to try some new therapies," he said. "And as long as they are not harmful, why shouldn't we try to do something, hopefully help some patients and learn from this?"
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