This show has taken a HUGE deviation from the comics. I am not sure how or when they will get back to the comics plot. It is pretty much a derivative work at this point.
I won't get into the "Scratching" but that will probably be revealed. I mean didn't both Rick and Shane basically bathe in zombie blood this last episode (with open wounds, no less...and rubbing their open wounds on things zombies had been licking)? That is much worse than being scratched. Think about it...