Prions popping up all over the place
The inflamed mammary glands of sheep have been found to contain protein particles that cause scrapie, a sickness similar to mad cow disease. This suggests that the suspect proteins, called prions, may also be present in the milk of infected animals.
If prions exist in the milk of cows infected with both an inflammatory illness and mad cow disease, formally known as bovine spongiform encephalopathy (BSE), this raises concerns for human health. Consumption of prion-contaminated meat from cows with BSE is believed to cause the fatal variant Creutzfeldt-Jakob disease (vCJD) in people; so might contaminated milk.
Man, that just opens up a whole new can o' worms. Pasteurization, which works well against bacteria, likely wouldn't put a dent in prion contamination in milk. Those suckers can survive full-out burning and still remain infectious.
The good news, though: so far, no prions have been found directly in the milk (though researchers expect to find them there in the future). Concentrations of prion in the mammary tissue was many times lower than that found in the brain. Additionally, prion presence in the mammary glands was correlated with infection by the Maedi Visna virus, so some other kind of infection may be necessary in order to have prion in that tissue.