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How effective is ZMapp? Human and non-human primate results differ

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The Ebola virus outbreak on the African continent has claimed hundreds of lives, and scientists are scrambling to find a treatment that is safe, effective, and manufacturable on the large scale required. According to a "near-final version" of an article in Nature, a monoclonal antibody-based treatment has shown promising results in non-human primates (NHPs). However, two of the four humans given the drug have died, leaving the drug's efficacy open to question. Moreover, the drug is expensive and time-consuming to manufacture.

On August 29, Nature made available a non-final version of a paper claiming that ZMapp, a humanized monoclonal antibody partially grown in tobacco plants by a small company known as Mapp Pharmaceutical, reversed the symptoms of Ebola in 18 macaques. These NHPs survived, despite some having been infected with Ebola as many as 11 days prior to receving ZMapp.

Two Americans who contracted Ebola in Africa and were flown to the US for treatment were also given ZMapp and also survived. Kent Brantly, a doctor, and Nancy Writebol, a volunteer, were treated at Emory University in Atlanta and recovered after several days. Although both were given ZMapp, they were also treated with IV hydration and other components of supportive care that exist in state-of-the-art American hospitals and not in Liberian field hospitals. Brantly also received a blood transfusion from an Ebola survivor while still in Africa. "If the question is, 'Did ZMapp do this?'" NIAID Director Anthony Fauci commented, "the answer is that we just don't know."

Indeed, both a Liberian doctor and a Spanish missionary who contracted Ebola and were given ZMapp died. The drug has not been approved or licensed by the FDA, but the World Health Organization (WHO) has issued a statement supporting the use of "unproven interventions with as-yet-unknown efficacy and adverse effects, as potential treatment or prevention." However, such unproven interventions appear to be limited in the United States to products developed by Mapp Pharmaceuticals and Tekmira, as the FDA has issued its own strongly worded statement against the use of natural products for Ebola prevention, calling these products "fraudulent."

There is no word yet on how the patients who received ZMapp in Africa have fared. What is known, however, is that Mapp Pharmaceutical's supply of the drug has been exhausted. Multinational drugmaker GSK plans to start its Ebola vaccine trials in humans this week.