Ebola Drug ZMapp Cured 18 Monkeys

How well the drug works in humans, however, isn’t so clear

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A rhesus macaque. Not one with ebola Yevgen Timashov/beyond/Corbis

There's some tentatively good news on the Ebola front. The experimental Ebola medication ZMapp—the one that was used during the successful recovery of two American healthcare workers—works remarkably well in monkeys infected with a strain of the virus.

According to a new study out today in Nature, researchers found that the Ebola medicine had a 100 percent cure rate when used to treat 18 rhesus macaques that had been infected with a lethal dose of the disease. The strain of Ebola tested in the study is not the same strain that's spreading across West Africa; they're close, but not identical.

Some of the macaques were already in relatively late stages of the disease, showing symptoms like hemorrhaging and high fever, and even they were pulled back from the brink. Importantly, the scientists found that the drug could be applied as late as five days after infection and still be effective. After five days, writes Thomas Geisbert in a news story for Nature, the symptoms of Ebola have already become obvious. Previous treatment approaches usually had to be applied before the patients showed any symptoms.

Of the 21 monkeys infected with Ebola, the 18 treated with ZMapp all recovered within 28 days. (The other three died.)

Now there are a couple caveats here before we get too excited about the prospect of ZMapp as an Ebola cure. For one, monkeys are not people. The two dead human healthcare workers who had also been dosed with the drug suggest that the medicine isn't a miracle cure for humans.

Whether Zmapp failed to cure the two dead healthcare workers is up in the air, though. It's possible the drug was just administered too late, says Geisbert. But, whether Zmapp had anything to do with the recovery of the two American healthcare workers, he writes, is also still up in the air. 

There's also the difference between the tested strain of Ebola and the Guinean variant currently spreading across West Africa. The researchers were able to show that, in a cell culture, Zmapp affected the Guinean variant. That's a sign that the drug could also be effective against this strain, too, but it's not enough information to say much for sure.

The best way to stop the spread of Ebola is still to prevent infection in the first place. Yet the lack of any effective treatment regiment means that infection is all too often a death sentence.

The fact that Zmapp shows so much promise, regardless of how tangential the research might be, suggests it's worth following up on. With Ebola's 90 percent fatality rate, a treatment doesn't have to be a miracle cure to be a better option than the status quo. 

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