Well the talking heads here in Wisconsin believe its possible to transmit CWD from deer to deer via saliva actually. Its basically a precaution to prevent "spit swapping" between deer that feed at a bait pile and therefore eliminate a possible transmitter of the CWD prion. Thats one of the reasons that I have come across at least. I'm sure there are a variety of different ways deer can transmit CWD through the herd but bait banningwas one potential way that would eliminate a potential transmission source. Hopefully that gives you a little idea on the thinking.....