I wish I had the answer to your question. I'm sure there are thousands of scientists out there that wish they had the answer to your question. When Creutzfeldt-Jakob Disease (Mad Cow disease, BSE) first exploded in Britain, I read a lot about it because I was intrigued by the disease. Apparently, it is similar to Alzheimer's in its effect on the brain. I haven't kept up on the research since then, but I'll tell you what I know. Jacob Crutchfield Disease is thought to be caused by prions, which are protein particles. Some scientists are still skeptical about whether prions are the cause of the disease or just a symptom of it because Jacob Crutchfield is the first disease ever discovered to be caused by protein particles instead of pathogens (viruses, bacteria, protozoans) or faulty.

(Creutzfeldt-Jakob Disease can also be caused by faulty genes or, seemingly, at random.) Somehow, and it is not known exactly how, prions can cause other proteins near them to change their shape. Normally, this requires some sort of genetic material (DNA, RNA), but prions do not contain genetic material. The disease can be spread easily when a sick cow enters the food supply because prions are not destroyed in the cooking process. They are not even destroyed in an autoclave, which reaches very high temperatures under extreme pressure (250-275 degrees F). This was the first protein found that can survive an autoclave without denaturing, or unfolding. (I guess scientists recently discovered another biological substance - an actual organism - that can survive an autoclave).

A protein's ability to withstand heat, gamma radiation, UV, acid, base or other chemical denaturing agents is determined by its "tertiary structure", or how it's folded. Apparently, a prions' tertiary structure is very, very sturdy, because only treatment with a very strong base can do the trick. Too bad for cows, sheep and humans!

Yes, you should be skeptical.

The idea behind prions is that they are proteins which have the same sequence of amino acids as some other protein that is useful in the body. Proteins, as enzymes, can cause chemical reactions to happen that normally wouldn't under with the temperature (etc.) present. A prion is able to take this biologically useful protein, and refold it into more of the prion (it can do this because the two proteins are the same molecule folded in different ways). The reason why this is dangerous to an animal's health is that it removes a protein that is essential for proper neural integrity of the animal. This protein apparently can survive the gauntlet of protein-destroying enzymes in the digestive system, and can thus get into the blood and ultimately the central nervous system of the animal that it is in, where it can do damage.

The "infectious" prion is apparently stable at high temperature as well as body temperature, so cooking it does not destroy it. As a result, it is dangerous to eat the meat from an animal that has this protein in its nervous system - in particular, it is dangerous to eat the nervous tissue of that animal (the muscle tissue is less likely to have the prion in it).

Anyhow, this is what I hear. Certainly a fair amount of the mad cow hype is hysteria; however, prions have been documented elsewhere, so it probably is a real health issue, although the statistics say that not many people die from it, even in the outbreak in England a few years ago.