The first US case of mad cow disease in six years was found in central California in a dairy cow that was not slaughtered for food. It has not been reported to be transmissable in milk. Testing of downer cows is only about 0.2%, so we cannot rest assured that Americans are not being exposed to a lot of cows that have the disease but are not yet sick enough to show the illness. The USDA should be ashamed of its record showing a massive inadequacy in screening meat that goes to market for human consumption.
On the other hand, there are only about 200 cases of mad cow disease in humans in the history of the disease. This is hardly an epidemic. While the disease has been attributed to a prion, the data supporting this assumption is very weak. We simply do not know the cause of mad cow disease. It has been suspected that the incubation period between exposure and the onset of clinical symptoms could be 10-20 years. This is a frightening thought!