The why is obvious. Exclusive rights to the profits of an invention.
So the is the real question is, "how"... unless the US actually invented ebola.
That's what you're getting at amirite?
That's the first thing that would come to mind but the patent was acquired in 2010. Ebola existed before then so this would have to be the invention of something like a bio-weapon. That is said to be the same as ebola plus it can be airborne. Why the CDC owns a patent, I'm still not so sure. One of the reasons I've seen much mention of is that it would be to help them find a vaccine for it and have exclusive rights to that vaccine but while the CDC is obviously in bed with the drug companies, who make billions off of vaccines, they do not, themselves, make vaccines nor would a US patent prevent any other country from making a vaccine.
But as we're in the midst of this outbreak, if you suddenly hear it can be transmitted through air, you know where it came from. And, of course, drug companies will make billions more on any vaccine for it that they put out there.