Mad Cow Disease and Variant Creutzfeldt-Jakob Disease
Mad Cow Disease and Variant Creutzfeldt-Jakob Disease Overview
"Mad cow" disease is an infectious disease in the brain of cattle caused by prions. The actual name of the disease is bovine spongiform encephalopathy (BSE), a name that refers to the changes seen in brain tissue of affected cows.
Abnormal proteins called prions (PRE-ons) are found in brain tissue of diseased cattle and appear to be the particle that transmits the infection. Characteristic changes are seen in the brain of infected cattle. Infection leads to tiny sponge-like holes in parts of the brain, giving the tissue a sponge-like appearance when viewed with a microscope. These so-called spongy holes cause slow deterioration within the cattle brain and eventually other symptoms affecting the whole body. Death follows.
If humans eat diseased tissue from cattle, they may develop the human form of mad cow disease known as variant Creutzfeldt-Jakob disease (vCJD) or new variant Creutzfeldt-Jakob disease (nvCJD). The disease was named after the researchers who first identified the classic condition. Creutzfeldt-Jakob disease in its classic form usually occurs in older people through an inherited tendency of the brain to change or the disease occurs spontaneously for no apparent reason. The type identified as occurring from eating diseased cattle occurs in younger people and has atypical clinical features, with prominent psychiatric or sensory symptoms at the time of clinical presentation and delayed onset of neurologic abnormalities. These neurologic abnormalities include ataxia within weeks or months, dementia (loss of memory and confusion) and myoclonus late in the illness, a duration of illness of at least six months, and a diffusely abnormal nondiagnostic electroencephalogram.
The transmissible agents that cause the disease in both cattle and humans are "prions." Prions are not like bacteria or viruses that cause other infectious diseases; rather, they are considered infectious abnormal proteins that are able to "induce abnormal folding of specific normal cellular proteins" according to the CDC. The CDC further states that the abnormal folding of proteins, especially in brain tissue, is responsible for the signs and symptoms of the disease.
The abnormal prions are found in the brain, spinal cord, eye (in the retina), and other tissues of the nervous system of affected animals or humans. In addition, prions can be found outside the nervous system in locations including bone marrow, spleen, and lymph nodes. Low levels of prions may also be found in blood.
Prions are highly resistant to heat, ultraviolet light, radiation, and disinfectants that normally kill viruses and bacteria. Prions may infect humans who eat meat from infected cattle. Even cooking meat infected with BSE does not eliminate the prions or the risk.
Once infection occurs, there is a long incubation period that typically lasts several years. When prions reach a critical level in the brain, symptoms such as depression, difficulty walking, and dementia occur and progress rapidly.
Scientists believe that BSE is transmitted from animals to humans when humans eat meat from infected animals. The content of infected brain tissue may be higher in some food products than others, and it may also depend on the way the animal was slaughtered.
BSE can be transmitted from one human to another through cannibalism or through transplantation of infected tissue. Consequently, certain human blood products and blood donations are not accepted from people who have lived in areas of the world where BSE outbreaks have occurred in cattle. BSE has been shown to be transmissible by blood transfusion in an experimental model using sheep. As of May 2011, the U.K. surveillance unit for vCJD had reported three cases of vCJD that occurred as a result of blood transfusion.
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Bovine spongiform encephalopathy (BSE), also known as mad cow disease, and variant Creutzfeldt-Jakob disease (CJD) are related disorders.