I think there could be some kind of virus that would make people BEHAVE like zombies. I'm not talking reanimation, just eating people/aggressiveness and all loss of humanity. Reanimation is a far fetch as well. But possibly if the front portion of the brain (where all our feral/motor controls are) was infected with a virus that killed you, then reanimated you by becoming its own living organism and instilling the need to feed (rhyme!). Perhaps then there could be a true, "Zombie Virus".
Read World War Z. I know its all fiction, but its pretty damn insightful and awesome. As well as the zombie survival guide.
And, look up Hierakanpolis. I don't know if the studies there a fluke or not, but its pretty interesting.
http://www.archaeology.org/online/features/hierakonpolis/zombies.html
Pretty sure its just a joke, but if not its pretty interesting. And sorry if this was posted already.