Mad Cow Disease caused a scare when it was first detected in 1986 in the United Kingdom. Although scientists are still not absolutely certain of what is causing the disease, called bovine spongiform encephalopathy, it is likely due to misfolded proteins called prions. Cooking does not destroy them, so when these prions are eaten by people or other animals, it probably transmits the disease.
Importantly, farmers stopped feeding meal that contained meat to cattle, which are herbivores and don’t need it anyway. Stringent precautionary measures were also put in place so that if the disease appeared in animals that were being raised as food, it would be detected before that food made it to the market. Indeed, it seems that the careful monitoring systems are working. A case has been identified in a cow in Scotland, which was removed before it could cause harm.