Mad Cow Disease and Variant Creutzfeldt-Jakob Disease

Mad Cow Disease Overview

"Mad cow" is an infectious disease in the brain of cattle. Humans who become infected, usually by eating tissue from diseased cattle, will die of a similar brain disease that may develop over many years.

Abnormal proteins called prions (PRE-ons) are found in brain tissue of diseased cattle. Prions eat away at the brain and create tiny spongelike holes in parts of the brain. These so-called spongy holes cause slow deterioration within the cattle brain, and eventually symptom affecting the whole body. Death follows. The scientific name for mad cow disease in cattle is called bovine spongiform encephalopathy (meaning sick brain) or BSE, meaning a sickness of the cow's brain; when damaged brain tissue is viewed on a laboratory slide, it has a spongy appearance.

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 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 6 months, and a diffusely abnormal non-diagnostic 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 infectious proteins. 

Diseased 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 including the 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.