It won’t be walking dead. It’ll be a virus that causes people to be brain dead but retain the instincts to forage and eat. They’ll mostly be democrats because a very weak virus will do the job
Or a fungus, like this one:
http://www.freerepublic.com/focus/f-news/2879822/posts
Zombie-ant fungus, which invades an ant's brain and causes it to march to its death at a mass grave near the ant colony, where the fungus spores erupt out of the ant's head.
The thread is complete with gross pictures!