Mad cow disease or bovine spongiform encephalopathy (BSE) is a degenerative, fatal brain disease of cattle that can be transferred. It is known to have a long incubation period of four to five years.

It is thought that the agent responsible for BSE is composed largely of self-replicating proteins (often called prions) which contaminate other proteins in the tissues of the animal. Another theory suggests that the agent is more like a virus.

Cattle infected with BSE exhibit typical symptoms of a neurological disease including lack of coordination, involuntary body movements, weakness of limbs and visual disturbances. The disease is fatal.

BSE is transmissible to humans and can be passed on when humans eat BSE-infected beef and beef products. The disease takes the form of a new variant of Creutzfeldt-Jakob disease (V-CJD) and has killed at least 80 people in the UK to date.

The European Union has moved to ban all cattle over 30 months old from entering the food chain unless test results prove that it is free from mad cow disease.

Most countries have banned the importation of beef and beef products from BSE-affected countries, as well as imports of livestock.

The World Health Organization of the United Nations announced in Dec 2000 that it would convene a major international meeting of animal disease experts and government officials on neuro-degenerative diseases affecting cattle and humans.

1. All countries must prohibit the use of ruminant tissue in ruminant feed and must exclude tissues that are likely to contain the BSE agent from any animal or human food chain.
2. All countries are encouraged to conduct risk assessments to determine if they are at risk for BSE in sheep and goats. It is advised that any tissue which may come from deer or elk with Chronic Wasting Disease (CWD, a transmissible spongiform disease of North American mile deer and elk) is not used in animal or human food. At this time however there is no evidence to suggest that CWD in deer or elk can be transmitted to humans.
3. No infectivity has yet been detected in skeletal tissue muscle. Reassurance can be provided by removal of visible nervous and lymphatic tissue from meat.
4. Milk and milk products are considered safe. Tallow and gelatin are considered safe if prepared by a manufacturing process, which has been shown experimentally to inactivate the transmissible agent.
5. Bovine materials for human and veterinary vaccines should be obtained from countries which have a surveillance system for BSE in place and which report either zero or only sporadic cases of BSE. These precautions apply to the manufacture of cosmetics as well.