The history channel just aired a show that talked about a possible "zombie like" infection that broke out during the black plague around 1350AD. The whole idea of flesh eating mindless zombies may have come from a real outbreak of a fungal paracite during a time when sanitation was ripe for disease and there was no knowledge of germs.
There's a new novel out that talks about this called "Life to the Dead" and the history channel show is called "Zombies: A Living History"
There are several types of infections that cause animals to behave like zombies: Cordycept fungi and this one are two:
http://www.npr.org/2011/10/30/141832...ling-parasites
There is some evidence that some of these infections can even animate seemingly dead organisms by "artificially perpetuating" parts of the organisms cells.