I have a feeling it's been in most states that it's being found in...all along. Just not been tested for until recently. Recently being, what, the last 10 years or so? Obviously, I have no factual info, just giving my opinion. That may be $.01 in this case.
you are correct since its naturally occurring in many species including humans. during our cwd committee work I asked the researchers that if cwd was detected in WI in 2002, how Long had it been in WI to reach detectable levels via random (small) sampling and that agreed and replied "many years"