Diseases & Conditions


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Bovine spongiform encephalopathy


The medical name for mad cow disease, a chronic, degenerative disease affecting the central nervous system of cattle. It is one of a group of fatal brain diseases called transmissible spongiform encephalopathies (TSEs). These infectious diseases, which are always fatal, create holes throughout the brain, making it look like a sponge. The first known TSE appeared in sheep, but now people, cows, elk, deer, mink, rats, mice, hamsters, and possibly monkeys all get various types of the disease. BSE was first identified in Britain in 1986, and was thought to be transmitted to humans via contaminated meat and bonemeal. The human version of BSE is called new variant Creutzfeldt-Jakob disease. As of November 2000 more than 177,500 cases of mad cow disease were confirmed in the United Kingdom alone in more than 35,000 herds; it had peaked in January 1993 at almost 1,000 new cases a week. The outbreak was caused by feeding tainted sheep meat and bonemeal to cattle, amplified by feeding rendered cow meat-and-bone meal to young calves. Since the feeding of bovine offal to cows was stopped in Britain, the incidence of the disease has declined significantly. Worldwide there have been more than 180,000 cases since the disease was first diagnosed in 1986. While there is a decline in the number of cases of BSE in the United Kingdom, confirmed cases of BSE have risen in other European countries, including Belgium, Czech Republic, Denmark, France, Germany, Greece, Ireland, Italy, Luxembourg, Liechtenstein, the Netherlands, Northern Ireland, Portugal, Spain, and Switzerland. More than 90 percent of all BSE cases have occurred in the United Kingdom. In the United States, officials restricted imports of live cattle and meat from countries with BSE in 1989. In December 2003 the first cases of mad cow disease was identified in a herd in Washington. No human cases in the United States have yet been diagnosed. The cause of BSE has been linked to three main theories: an unconventional virus, an abnormal prion, or a virino (“incomplete” virus) composed of naked nucleic acid protected by host proteins. What scientists do know is that the BSE agent is smaller than most viral particles and is highly resistant to heat, ultraviolet light, ionizing radiation, and common disinfectants that normally inactivate viruses or bacteria. They also know that it causes no detectable immune or inflammatory response and has not been observed microscopically. At present, most scientists blame prions as the most likely cause. There is no test to detect the disease in a live animal, but two lab methods can confirm a diagnosis of BSE on autopsy: microscopic examination of the brain tissue to identify characteristic changes or techniques that detect the prion.