I am gonna get a bit technical here. But if anybody wants a good understanding of how virus like this "behave", I suggest reading "The Hot Zone", by Richard Preston.
Most "plagues" take one of two forms. Viral, and Bacteriological. And of these two, the Bacteria are generally the lowest threat. They can spread fast, and in a "virgin field" can be devastating. But proper sanitation and fast vaccination has largely nullified this threat.
It is the virus that causes the most problems now. And the pockets where most of them originate tends to be rainforests and other similarly dense areas. Ebola, Corona, Avian Flu, all of these are classic rainforest type diseases. And in places where humans are finally starting to operate more actively, they are finally coming into contact with them.
Most of the dense forested areas of China were largely "off limits" for millennia. The same with Africa, Philippines, and many other areas of the world. And as humans are now entering them, the contact with these is increasing.
And the hardest thing to research is that in many cases we still do not know what the vector is that spreads these diseases. Mosquitos, fleas, rats, flies, there is normally some kind of vector that spreads it. And normally the disease does not affect them, or affects them very slowly.
For Ebola, we have been searching for decades and still do not know what the disease vector is. Bats are one of the leading suspects (the area the disease breaks out is always an area with a high bat population), but that is still only a theory. And the fact that it has been found in both Africa and the Philippines has caused many to wonder exactly how old it is, and why it was only discovered some 45 years ago.
I think the thing I find most interesting is that while we have had huge outbreaks of these kinds of diseases from Asia and Africa, very few seem to have come out of Central and South America.
And of course, writing about the end of the world because of a virus is not new. 42 years ago Stephen King introduced us to "Captain Trips" in "The Stand".