Mad Cow Disease: Sounds like some cheap marketing gimmick that's peddling "radical awesome-burgers" in a McDonald's happy meal aimed at the "tween" demographic. It's anything but that.
One doomsday scenario not mentioned in Robert Brockway's book is something which may well be incubating within every non-vegetarian on the planet, thanks to tainted beef.
Cannibalism is the main cause: Kuru; Mad Cow Disease (from cows unwittingly eating other cows); C-J cause unknown
Prions not living
Reproduce like "Ice-9."