While there is always more to be said, there are significant doubts as to whether the Black Death did originate very far to the east of where it was first reported, in the lands of the Golden Horde. I discussed what can be said about its origins and lethality in an earlier thread, here

Why can't I find very much information about the 14th Century Black Death in Asia?

and you might like to review that while you wait for fresh answers to your question.