Bovine spongiform encephalopathy (BSE), commonly known as "mad cow disease," is a fatal disease that strikes the nervous system of cattle. Currently, no vaccine or treatment exists to treat BSE, and affected animals display a variety of neurological symptoms before they die (think of television reports showing cows having trouble standing up).
An animal with outward symptoms of BSE may survive for 2 weeks to 6 months, though it may have carried the disease for up to 8 years. BSE has an incubation period (the time between infection and development of symptoms) ranging from 30 months to 8 years, which is a long time for a disease to remain undetected.
BSE is a disease that only cows develop; however, it is related to a "brain-wasting" disease that affects humans, called Creutzfeldt-Jakob disease (CJD). CJD occurs due to a spontaneous genetic mutation that occurs in one in every million individuals. In 1996, another form of CJD was identified and has since been named "variant CJD" (vCJD). This variant form of CJD has been linked to the consumption of meat products infected with BSE.
Scientists believe that BSE is most often spread through the practice of feeding cattle various meats (rendered material) from slaughtered animals such as sheep, goats, and other cattle.
During this process, an abnormal protein that is linked to BSE can spread from a slaughtered diseased animal to a healthy one. This abnormal protein, called a prion, can withstand high temperatures and does not get destroyed during the rendering procedure. Since the incubation period for BSE is so long, it is possible for an infected animal to enter the food chain before the symptoms appear.
Proteins are long molecules that are folded up into particular shapes. A prion is folded differently from a normal protein, and it can cause normal proteins to change and fold abnormally. When this happens, the proteins (normally found in liquid form in cells) begin to solidify.
The cells most often infected are the brain cells. The resulting solidification of the proteins causes the infected brain tissues to look like a sponge with several tiny holes, hence the name "spongiform encephalopathy."
Because BSE damages the brain tissue, it has a variety of symptoms ranging from behavioural changes to coordination problems. Cows with BSE may show nervousness or aggressive behaviour, difficulty with coordination, trouble standing up, decreased milk production, and weight loss. The disease is fatal, with death usually occurring 2 weeks to 6 months after symptoms start.
In humans, both CJD and vCJD are also fatal conditions, with death occurring 6 to 24 months after symptoms first appear.