Zombies for me are corpses animated by voodoo or other mumbo jumbo sinister dark magic. I don't consider many of the ''zombie'' flicks today about zombies. More are just about people driven to the intelligence level of a carrot, paired with the violence and rage of a hormonal Predator.
Or simply, human rabies. They're alive, but mad, bad and dangerous. Is your dog with rabies a zombie? No.
I would say corpses reanimated by diseases can to a certain extent be classified as zombies tjough.