I was called in to consult on an issue in a cattle processing facility in eastern Georgia a while back. I think I've talked about it before, but it was something I've never forgotten. The sounds of the cattle going up the chute to the "stunner", the look in their eyes, and the way the product was processed.
In regard to the "nerve tissue", the spine was cut in half lengthwise (along with the carcass) and the cord "picked out" and discarded on the floor. Obviously the blade passed through the entire carcass. The halves were hosed down with a solution (I wasn't told what it was - wasn't relevant to what I was called in for), and the halves continued down the production line.
I know nothing about prions, and where they are distributed in nerve tissue. I just hope the FDA and CDC stay on top of this. The facility I saw processed thousands of cattle daily. If cross-contamination can occur, then our safety is dependent on the honesty and work ethic of the lowest paid workers in this type of facility.