The Facts

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 for it, 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 to 6 months, though it may have carried the disease for up to 6 years. BSE has a longer-than-usual incubation period (i.e., the time between infection and development of symptoms), ranging from 3 to 6 years - a long period of time for it to remain undetected.

BSE is a disease that only cows develop; however, it is related to a 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. Recently, a new form of CJD has emerged and has been called "variant CJD" (vCJD). This new form of the disease has been linked to the consumption of meat products infected with BSE.

Causes

Scientists believe that BSE is most often spread through the practice of feeding cattle various meat (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.

All proteins are long molecules folded up into particular shapes. A prion is folded differently from the normal protein. What's more, it has the ability to make normal proteins that touch it fold in the same abnormal way. When this happens, the proteins, which are normally in liquid form, begin to solidify within the cells. The cells most often infected are the brain cells. The resulting solidification of the proteins causes the infected brain tissue to look like a sponge with several tiny holes, hence the name spongiform encephalopathy.

This is a completely new form of disease. It is caused by an infectious agent that's not alive but is capable of multiplying.

Symptoms and Complications

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 to 6 months after symptoms start.

In humans, both CJD and vCJD are also always fatal conditions, with death occurring 6 to 24 months after symptoms appear.

Making the Diagnosis

Live animals cannot be tested for the disease. The only way to confirm the presence of BSE is by checking the brain tissue of an animal after it dies. Upon examination, the brain is found to be full of small holes, like a sponge. That's why this disease is called spongiform.

In humans, a genetic test exists to determine if a person might be susceptible to vCJD, but here too, the only way to confirm the diagnosis is through a sample of brain tissue obtained on biopsy or autopsy.

Treatment and Prevention

There is no cure, treatment, or vaccine for BSE.

The best way to prevent the disease is to avoid feeding cattle rendered material from slaughtered animals, and to isolate and destroy all infected animals. There are currently no BSE epidemics in Britain or anywhere else, although two reports of infected cows recently occurred in North America. Most countries have developed policies for monitoring BSE in their cattle herds and procedures for dealing promptly and thoroughly with BSE cases when they do arise.

Canada is taking the following steps to prevent the spread of BSE:

• Health Canada is working closely with the Canadian Food Inspection Agency (CFIA) as part of the Agency's National Response Team.
• Health Canada is assessing the implications of BSE and the emerging information from the trace back studies.
• The Canadian Food Inspection Agency (CFIA) has taken various precautions to prevent the introduction and spread of BSE, including creating a surveillance program in which the brains of cattle are tested for the disease.
• Since 1997, Canada has banned the feeding of rendered protein products from ruminant animals (cattle, sheep, goats, bison, elk, or deer) to other ruminants.
• The CFIA has mandated that all suspected BSE cases be reported to a federal veterinarian. The CFIA has also created a Canadian Cattle Identification Program for cattle and bison, making it possible to trace individual animal movements from the herd of origin to the time of slaughter.

There is no cure, treatment, or vaccine for CJD or vCJD.