[Jack Simth]

Last I heard, the current working hypothesis on what exactly causes BSE (several months ago, at least; some of this could be off):

A single protien, a warped form of one occuring naturally in most mammals. Specifically, the protien is warped in such a way that when it encounters the normal Version, it warps the normal Version into the warped Version. Unfortunately, the normal protien is necessary for nerve function, and the warped Version doesn't do that function. As a single protien, we don't know of any method to destroy them all. Heat will destroy some, but not all, of them. Chemicals will destroy some, but not all, of them. Radiation will destroy some, but not all, of them. Unfortunately, one is all it takes. Cooking infected meat won't help much.