"Mad cow disease"-also known as bovine spongiform encephalopathy (BSE)-is a fatal brain disorder in cows. It's spread by contact with brain or other nervous-system tissue from an animal with the disease. An animal can be infected but not have any symptoms for years. But once the disease is active, it kills brain cells, leaving large, spongy holes. It also causes large clumps of abnormal proteins in the brain and quickly kills the victim.
Scientists still don't know for sure what causes mad cow disease. But the most likely theory is that abnormal proteins called prions (PREE-ons) damage nerve cells, causing loss of brain function and eventual death.
You can read more about prions and how scientists think they might cause mad cow disease:
Scientists think mad cow disease came from a similar disease in sheep called scrapie. We used to feed cows meat and bone meal-from other cows, but also animals such as sheep-leftover after processing for human consumption. Cows ate food contaminated with scrapie and developed BSE. At the time, people thought that neither scrapie nor BSE affected us, so meat from BSE-infected cows got into the human food supply. People who ate the infected meat-probably hamburger or other processed meats-developed a disease similar to the cows'.
You can find out a lot more about mad cow disease and its human manifestation:
The US government has made some rules to try and protect people here from the disease. It has banned the import of cud-chewing animals (cows, sheep, goats) and products made from them from Europe. It prohibits the use of any mammal products in food for cows. Cows with unidentified neurological disorders cannot be eaten. Drug companies can't use animal tissues from countries with mad cow disease when they make vaccines or other products. And people who spent more than six months in the UK (where the mad cow disease epidemic was first identified) between 1980 and 1986 are not allowed to donate blood.
Do the new rules make you feel safer about eating meat? Have you changed any of your eating habits since mad cow reports came out in the media?