Bovine spongiform encephalopathy

Bovine spongiform encephalopathy (more commonly BSE or mad cow disease) is a fatal neurodegenerative disease of cattle part of the Transmissible spongiform encephalopathy family of diseases. BSE is believed to be caused by prions and to have evolved from the sheep prion disease scrapie through the use of sheep protein in animal feed for cattle. One of the kinds of the human prion disease, Creutzfeldt-Jakob Disease, is thought to be transmitted to humans through the ingestion of beef contaminated with BSE. Another related prion based disease found in Deer and Elk is Chronic Wasting Disease (CWD).

Eating meat from cattle with BSE is thought to have caused the new variant of Creutzfeldt-Jakob disease (nvCJD) in about 131 cases (2003 june data) in the United Kingdom and some few in France. Rodents injected with brain tissue obtained from cows with BSE develop a fatal neurological disorder in one or two years.

It is possible to detect the abnormal prion protein in some, but not all, of these animals' brain tissues. Although there is substantial evidence for transmission of the disease by prions, and various theories have developed about the absorption of prion proteins by intestinal cells, there is still no definite proof reliably showing that eating infected beef is really the cause of the new variant Creutzfeldt-Jakob disease.

There is also some concern about those who work with (and therefore inhale) cattle meat and bone meal, such as horticulturists[?] who use it as fertilizer. The first BSE epidemic was recognized in the United Kingdom in 1986.

BSE is thought to have arisen from cattle fed with a high-protein diet, obtained from the remnants of butchered animals and modified using methods developed in the early 1980s. This practice allowed the accumulation of prions over many generations.

The use of animal byproducts as a protein supplement in cattle feed was widespread in Europe prior to the early 1980s. Soybean meal is the primary plant-based protein supplement fed to cattle, and soybeans do not grow well in Europe. This means high costs, and cattlemen throughout Europe turned to the less expensive animal byproduct feeds as an alternative.

Soybean meal is cheap and plentiful in the United States. As a result, the use of animal byproduct feeds was never as common there as it was in Europe. U.S. federal regulations have prohibited the use of animal byproducts in feed for ruminants for some years now. The USDA now estimates that, should BSE occur in the U.S. cattle herd, it would die out of its own accord rather than spreading due to these restrictions.

Although at least two cases of BSE have occurred in North America, no cases have been found in the United States to date (2003), nor has a case of new-variant Creutzfeldt-Jakob Disease occurred so far except among those who have travelled to Europe.

The most recent case of BSE in North America was reported in Canada on May 20, 2003. It occurred in a single older cow that may have contracted the disease from contaminated feed in earlier years. The animal had been destroyed and declared unfit for consumption prior to being diagnosed. The United States issued a temporary ban on all Canadian beef. The last North American case of BSE was in 1993 involving an animal born in Britain.