Bovine spongiform encephalopathy, commonly called "mad cow disease" or BSE, is a fatal degenerative disease of the central nervous system in cattle. The disease is thought to be caused by an abnormal protein found in the central nervous sytem called a prion. BSE is one of several transmissible spongiform encephalopathies that afflict different species of mammals. The common element among them is that they leave the brains of their victims with lesions that make them look like sponges when viewed under a microscope after death. Although the diseases may have slightly different symptoms and may be transmitted differently, all affect their victims' coordination and movement, and all are fatal.
Other transmissible encephalopathies have been found in species including cervids (chronic wasting disease), mink (TME) and felines.
The United States takes a multi-pronged approach to preventing BSE: banning certain imports, banning suspect feed ingredients, testing for the disease, banning nonambulatory animals from slaughter, and banning risky animal tissues from human food.
Clinical Signs of Illness
Clinical signs of BSE may include:
- Behavioral changes such as aggression or nervousness
- Abnormal posture
- Lack of coordination
- Inability or difficulty in rising or walking
- Decreased milk production
- Weight loss with normal appetite
BSE is always fatal, normally within two weeks to six months after the signs first appear. However, the animal may be infected from two to eight years before showing clinical signs. This time is called the incubation period.
There is no test for BSE in live animals; the only way to diagnose it definitively is to examine tissue from the animal's brain under a microscope for the telltale sponge-like lesions.
There is no treatment for BSE.
New-variant Creutzfeldt-Jakob disease (nv-CJD) is a human disease of the central nervous system that was first diagnosed in the United Kingdom in 1995. Scientists have linked the disease to eating meat products from cattle infected with bovine spongiform encephalopathy, commonly called mad cow disease.
It's important to understand why it's called "new variant," as opposed to "classic" Creutzfeldt-Jakob.
Classic CJD has always been with us. It's very rare, striking about 1 person in a million every year, worldwide. Mostly these cases are "sporadic," meaning they have no known cause. A few have been linked to organ transplants from infected people, or to genetics. Americans die from classic CJD, but they do not contract it from contaminated meat. Classic CJD strikes people 50 or older, progresses rapidly, and has only physical symptoms.
Except for a few cases in other European nations with BSE, nv-CJD has been found almost exclusively in the United Kingdom. It strikes younger people, often begins with psychiatric symptoms, and progresses slowly. Unlike classic CJD, nv-CJD has been linked to eating meat products from cattle that had BSE. Also unlike classic CJD, nv-CJD cases increased for a number of years, although the number per year now appears to be dropping off in the United Kingdom as the result of preventive action. From the original 3 cases in 1995, numbers per year grew to 27 in 2000, but only 7 cases have been confirmed in the first half of 2001. As of June 29, 2001, authorities had counted 102 definite and probable cases of nv-CJD in the United Kingdom. In the United States, there has been only one known case of nv-CJD. A Florida woman died in June 2004 after eating BSE-contaminated beef more than a decade ago in England.
Both diseases eventually destroy victims' motor skills and coordination, and both show the characteristic spongelike appearance in their victims' brains when autopsiedand both are fatal.