Bovine spongiform encephalopathy (BSE), commonly known as mad cow disease, is a fatal neurodegenerative disease (encephalopathy) in cattle that causes a spongy degeneration in the brain and spinal cord. BSE has a long incubation period, about 30 months to 8 years, usually affecting adult cattle at a peak age onset of four to five years, all breeds being equally susceptible. In the United Kingdom, the country worst affected, more than 180,000 cattle have been infected and 4.4 million slaughtered during the eradication program.
The disease may be most easily transmitted to human beings by eating food contaminated with the brain, spinal cord or digestive tract of infected carcasses. However, it should also be noted that the infectious agent, although most highly concentrated in nervous tissue, can be found in virtually all tissues throughout the body, including blood. In humans, it is known as new variant Creutzfeldt–Jakob disease (vCJD or nvCJD), and by October 2009, it had killed 166 people in the United Kingdom, and 44 elsewhere. Between 460,000 and 482,000 BSE-infected animals had entered the human food chain before controls on high-risk offal were introduced in 1989.
A British and Irish inquiry into BSE concluded the epizootic was caused by cattle, which are normally herbivores, being fed the remains of other cattle in the form of meat and bone meal (MBM), which caused the infectious agent to spread. The cause of BSE may be from the contamination of MBM from sheep with scrapie that were processed in the same slaughterhouse. The epidemic was probably accelerated by the recycling of infected bovine tissues prior to the recognition of BSE. The origin of the disease itself remains unknown. The infectious agent is distinctive for the high temperatures at which it remains viable; this contributed to the spread of the disease in the United Kingdom, which had reduced the temperatures used during its rendering process. Another contributory factor was the feeding of infected protein supplements to very young calves.
The first reported case in North America was in December 1993 from Alberta, Canada.
Another case reported later in May 2003. The first known U.S. occurrence came in December of the same year, though it was later confirmed to be a cow of Canadian origin imported to the U.S. Canada announced two additional cases of BSE from Alberta in early 2005. In June 2005, Dr. John Clifford, chief veterinary officer for the United States Department of Agriculture animal health inspection service, confirmed a fully domestic case of BSE in Texas.
A new case of BSE disease was recently found in a dairy cow on 23 April 2012 in California during a planned Agriculture Department surveillance program.
On 8 December 2012, the Japanese government issued a ban on imports of raw beef from Brazil, based on reports that a cow which died in 2010 in southern Brazil carried disease-carrying proteins. The Brazilian Ministry of Agriculture maintains that its beef is free of BSE. The Brazilian Ministry of Agriculture informed that the animal in question didn't manifest the disease and didn't die of this cause.