In a recent issue of the Journal of Pathology (volume 209, page 4), Dr. Martin Jeffrey of the UK Veterinary Laboratories Agency in Penicuik, Modlothian, proposes that prions ingested from the meat of infected animals is not a cause of Bovine Spongiform Encephalitis or CJD. 

His proposal, which is highly controversial, claims that the prions found in the infected meat are destroyed by stomach acids and never seem to make it into the body.  Still, out of the 50 sheep studied in his experiment, 3 developed scrapie (the ovine version of the disease) even though no prions from the stomach of the sheep survived.  This suggests another ingredient may be responsible and possibly that there is a genetic component that makes one person more susceptible than another to the disease.

More research needs to be funneled in this direction to get to the bottom of these puzzling diseases as it may help us understand other neurological disorders as well.