mouse models, raising concern for cattle and sheep. See this article on research by Nobel Prize winning researcher:
Muscle and flesh of cattle and sheep may harbour deadly levels of prions that cause variant CJD. This stark prospect, raised by the Nobel Prize winner who first discovered that these infective particles can cause brain illnesses, suggests eating meat may still pose a serious health risk.
http://www.guardian.co.uk/bse/article/0,2763,851547,00.htmlWe just can not say for sure at this point.