[Baron Munchausen]

Yep, BSE is caused by a prion. It developed from scrapie, a similar disease in sheep, because of the practice of feeding the rendered leftovers of slaughter to other livestock. Admittedly it took a while, so prion diseases are not easily transmissible from one species to another, but it does occur. Similarly, the largest spike in 'variant CJD' in the world is currently occuring in Britain where they had this huge problem with BSE. It's small by epidemic standards (a few hundred cases) but quite signifigant in proportional terms. This is the reason for the strict standards in US livestock industry forbidding feeding the remains of animals to other animals.