It's based on the black plague era "zombie like" parasitic infection that may have lead to the whole idea of zombies in the first place. I've heard recently that the idea of flesh eating mindless humans comes from the memory of people that were infected with a type of parasitic fungus that controls the body and brain in order to feed itself and find new hosts. It kind of makes sense because 14th century London was a very unsanitary place where people didn't know anything about germs and the whole idea of demon possession was popular. One demon, known as Eurynome, came from that era and was called the eater of corpses.
http://m.npr.org/story/141832947?url...ling-parasites
http://www.amazon.com/Life-Dead-Seth...0002862&sr=8-1