no! No! NO!! NO Viruses!!!!
OOoooooOOoo! Be patient! I have it ALL figured out!
Pathogens do not, can not and will NEVER effect dead tissue. Pure and simple.
There is an alternate mechanism by which the Undead are reanimated which circumvents and is independent of biological pathways. It explains everything from the fact that the Walking Dead reanimate in the first place and includes explanations for why they crave human flesh, acquire a decayed appearance so rapidly and even identifies why some zombies seem to function at different levels of intelligence, a few even seeming to maintain a slight concept of "self" and perhaps vague memories. I've even worked out why the bite kills--WITHOUT the fall-back of a "virus".
The Rise of the Walking Dead was a WORLD-WIDE event that manifested simultaneously across the planet. No pathogen can do that. The situation requires the presence of an element already in the environment which is then activated by another factor. Once the Dead rise, then, yes, those people dying from bites would form a spread constellation similar to that of a highly virulent contagion, but that is misleading. There was a direct Cause/Effect incident that created the situation and it operates on a non-biological principle. At least, it is not bio-CHEMICALLY based.
Be patient. I'm putting it all together in my short book.