I beleive the disease specalist make guesses the latest is cwd is spread by crows.i have watched the process for several years and at best to date are simply a guess.Culls/ head collection/ to date has led the parade by the specalist.The cull programme has killed far more deer that cwd ever will.In alberta resident hunters have no confidence in the fish and wildlife and don't support the new releasted cull programmes. At the rate we are going the culls will iradicate the deer.