I’m wondering why America had been as “lucky” as it was with respect to Ebola. This is a world in constant contact. There is no countrywide quarantine on Liberia. Hands that shook hands with Ebola carriers probably have been in the USA for years if not decades.
Perhaps there are other factors that influence an attack of Ebola to be specially deadly, factors that are present in Africa. Without such a factor present, perhaps the sufferer usually survives and nobody knows it was not a common flu.
Several researchers have become infected over the years. I don’t think Americans have any special immunity. As for Ebola carriers, they would either recover or die. Most that recover would have shown some serious symptoms along with way. They would know and would not mistake it for the flu. But they could be around carrying both viruses and antibodies for some period.
Symptoms of Ebola are not much different than a serious attack of flu. Thousands of Americans die from flu every year. May be Ebola can go undiagnosed in many cases.