First of all, Zmapp is NOT a cure. It's an experimental drug. Second, Ebola didn't make it to the US before this "cure" was "mysteriously found". All seven of the people given Zmapp caught the virus in Africa. Two Americans, three Liberians, a Spanish priest and a British nurse. The Americans and the Brit survived because they were treated in state of the art medical facilities. Out of the four others, two of them still died (one of them a Liberian doctor). That doesn't sound like a much of a cure to me.
Basically, Zmapp is something that could effectively treat Ebola, but the patient probably would be best served being treated under ideal conditions. Also, with such a small sample size, it's impossible to call it a cure. It needs a lot more testing to get approval as such.