Nebraska (formerly known as the Beef State) Department of Agriculture Director Greg Ibach, thinks the Feds will get this straightened out before the Japanese ban's effects trickle down to the Feedlot. Other government and industry folks are also trying to put a lid on concerns about Mad Cow in the US. Nothing to worry about.
You know spinal cord tissue as that greasy stuff you sometimes find in a small depression at the point where the 'T' is crossed on a T-Bone steak:
There are numerous taxonomically differentiated forms, largely because the symptomology was observed in various species and locations long before the prion connection was made. When people get it, the docs call it Variant Creutzfeld-Jacob disease. (To distinguish it from the Classic CJD, which isn't related to cow eating, I guess.) The first human form was noted among Pacific island cannibals, where it was called Kuru. In sheep the prion problem is called Scrapie, and in our own native deer it is called Chronic Wasting Disease, (CWD). In all cases, the victim's brain, human or animal, winds up looking like swiss cheese. In humans the victim dies a stumbling, mumbling idiot. As a class, these afflictions are known as Transmissible Spongiform Encephalopathies (TSE).
If, after reading the links above, you believe science really knows how this nasty condition spreads, you are naive. If you believe that bad prions know to stay only in the infected cow's spinal cord and out of the rest of the nerves you can't see, then you are as dumb as the USDA thinks you are. And if you believe that the whole TSE problem isn't being deliberately obfuscated for political and economic reasons, then I have a footbridge in Nebraska to sell you. No worries?
Update on CWD in deer: prions found in deer meat (venison), not just in central nervous system.