Ebola-infected monkeys that were given an experimental treatment being developed by Canadian researchers have all recovered fully, a paper published Friday says.
The antibody cocktail will now be tested on humans in a rush to find an effective treatment or cure as the largest Ebola outbreak in history continues in West Africa, though the treatment is still almost a year away from being used in the field.
The treatment, a blend of three antibodies called ZMapp, was given to monkeys infected with Ebola. All of the 18 rhesus macaques treated recovered fully, even those treated as late as five days after infection. It reversed all symptoms, including fever, excessive bleeding, rashes and elevated liver enzymes. The three monkeys that were infected but did not receive treatment died within eight days, according to the paper published online in Nature.
"It worked fantastically well," said Gary Kobinger, one of the researchers in the study and a professor at the University of Manitoba. "We of course expected an improvement. We were hoping for it. But the level of improvement was actually beyond my own expectations. I was quite surprised."
ZMapp was developed based on previous trials, the results of which were used to select the most effective combination of antibodies to fight the virus after infection.
The incubation period for Ebola is different in humans than in other primates, Dr. Kobinger said. While humans may not show any symptoms until as late as 21 days, all of the monkeys in the trial had a fever and other clinical symptoms within five days of becoming infected. Dr. Kobinger said humans would probably have the same amount of the virus in their system roughly nine to 11 days after becoming infected, though it is difficult to translate between species.
Dr. Kobinger said human trials on ZMapp will begin early next year and, if the results are positive, used in the field to treat Ebola by next summer.
"If there is a safety [trial] in early 2015 and the data is released before the spring, there's a possibility," he said.
Six individuals who contracted Ebola were given ZMapp as a last-ditch effort to save them earlier this summer. Two survived, two died and there has not been an update on the other two.
Dr. Kobinger said while there isn't enough information on these cases to draw a conclusion, there are several possibilities for why the drug succeeded in some cases and failed in others.
"We know at one point there is a point of no return where there is too much damage in the major organs [for the drug to be effective] and that's just the reality of it," he said. "There are other things, as well, that come into play. There is the age, the timing, the general health of the person."
He was not sure whether more treatments would be administered in the field while trials continue, but he noted that more antibodies need to be produced.