ZMapp cures monkeys of Ebola virus

American Ebola patient Nancy Writebol, pictured here being wheeled into Emory University Hospital in Atlanta on Aug. 5, 2014, received several doses of the experimental serum ZMapp.

The experimental Ebola drug known as ZMapp has healed all 18 monkeys infected with the deadly virus in a new study. If subsequent studies prove as promising, the treatment may help fight the outbreak raging through West Africa -- once more of the drug can be made.

For the study, published online Friday by the journal Nature, researchers gave the monkeys ZMapp three to five days after they were infected with the virus and when most were already showing symptoms. That is several days later than any other experimental Ebola treatment tested so far.

"For animal data, it's extremely impressive," said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, which had a role in the work.

In another study, the drug also completely protected six other monkeys given a slightly different version of it three days after infection in a pilot test. These two studies are the first monkey tests ever done on ZMapp, which is a compound of three antibodies that attach to cells infected with Ebola, helping the immune system kill them.

It's not known how well the drug would work in people, who can take up to 21 days to show symptoms and are not infected the way these monkeys were in a lab. Several experts said it's not possible to estimate a window of opportunity for treating people, but that it was encouraging that the animals recovered when treated even after advanced disease developed.

Primates have been good stand-ins for people for many viral diseases, but how well they predict human responses to Ebola, "we just don't know," said Dr. Cameron Wolfe, a Duke University infectious disease specialist. The study also "tells us nothing about side effects" people might have, he added.

ZMapp had never been tested in humans before two Americans aid workers, Nancy Writebol and Dr. Kent Brantly, who got Ebola while working in Africa were allowed to try it. Both of them recovered. The rest of the limited supply was given to five others. In recent weeks, the use of the untested drug on a limited number of patients has incited an ethical dilemma over who should get it.

Of the seven people known to have been treated with ZMapp, two have died -- a Liberian doctor and a Spanish priest. The priest received only one of three planned doses. Two Africans who received ZMapp in Liberia -- a Congolese doctor and a Liberian physician's assistant who were expected to be released from a treatment center on Friday. A British nurse also got the drug, reportedly the two unused doses left over from treating the Spanish priest.

There is no more ZMapp now, and once a new batch is ready, it still needs some basic tests before it can be tried again during the African outbreak, Fauci said. "We do need to know what the proper dose is" in people and that it's safe, he said.

ZMapp's maker, Mapp Biopharmaceutical Inc., of San Diego, has said that it will take several months to make more. The drug is grown in tobacco plants and was developed with U.S. government support.

Gary Kobinger, a professor at Public Health Agency of Canada in Winnipeg and lead author of the ZMapp study, said it takes about a month to make 20 to 40 doses at a Kentucky plant where the drug is being produced. Officials have said they are looking at other facilities and other ways to ramp up production, and Kobinger said there were plans for a clinical trial to test ZMapp in people early next year.

"The treatment window in humans needs to be established in a well-controlled trial" that also would explore the correct dose of ZMapp in people," Erica Ollmann Saphire, a Scripps Research Institute professor who has worked with some of the study leaders on antibodies to Ebola, wrote in an email. "Given its tremendous efficacy in the nonhuman primates, I don't see how it couldn't be helpful in people."

Ebola has killed more than 1,500 people this year and the World Health Organization says there could be as many as 20,000 cases before the outbreak is brought under control. On Friday, it spread to a fifth African country -- Senegal, where a university student who traveled there from Guinea was being treated.

There is no approved vaccine or specific treatment for Ebola, just supportive care to keep them hydrated and nourished. Efforts have focused on finding cases and tracking their contacts to limit the disease, which spreads through contact with blood and other fluids. However, on Thursday, U.S. federal health officials announced they plan next week to start a human trial on an Ebola vaccine that's proved to be promising when tested on animals.

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