However, last week we reviewed indirect evidence indicating that some cows in the U.S. may already have mad cow disease and that some people in the U.S. may already have a human version of the disease. In this country, there is some evidence that CJD may not be as rare as was once thought because some cases of CJD may have been misdiagnosed as Alzheimer's disease. Mad cow disease is one of a family of diseases called transmissible spongiform encephalopathies, or TSEs for short. Prions are normal proteins, present in all mammals and some non-mammalian species such as salmon and ostriches. According to the prion theory of disease, some prions can fold abnormally and then they can kill nerve cells.
Prions are remarkably hardy.
They are not destroyed by the digestive system of humans or other animals. And they are very heat resistant. Prions are hard to stop. Under FDA's rule, ruminants can be fed to pigs and pigs can be fed to ruminants. Under the rule, even ruminants that are known to be infected with a TSE can be fed to pigs.