Bovine Spongiform Encephalopathy | The Canadian Encyclopedia


Bovine Spongiform Encephalopathy

Bovine Spongiform Encephalopathy (BSE), frequently called "mad cow disease," is a progressive, fatal disease of the nervous system of cattle.

Bovine Spongiform Encephalopathy

Bovine Spongiform Encephalopathy (BSE), frequently called "mad cow disease," is a progressive, fatal disease of the nervous system of cattle. It is one of a family of related diseases, which includes scrapie in sheep, chronic wasting disease in deer and elk, and Creutzfeldt-Jakob disease (CJD) in humans. Although the exact cause of BSE is unknown, it is associated with the presence of an abnormal protein called a "prion." There is no treatment or vaccine currently available for the disease.

BSE is not contagious - it is not transmitted from one living animal to another. Researchers believe it is spread when a susceptible animal consumes feed that has been contaminated with infective material. From a disease control perspective, one of the more challenging characteristics of the BSE prion is that it is not destroyed through processes used in producing animal feed, such as high-temperature cooking.

BSE is an unusual disease in that the time between an animal's exposure to the disease and the onset of clinical signs normally ranges from 4 to 5 years. Animals with BSE may show a number of different symptoms including nervous or aggressive behavior, abnormal posture, lack of co-ordination or difficulty in rising from a lying position, decreased milk production, and weight loss despite an increased appetite. These symptoms may last for a period of 2 to 6 months before the animal dies.

BSE was first recognized and defined in cattle in 1986 in the UK. It may never be possible to determine exactly when and where the disease originated. Some scientists believe that the BSE prion originated from the scrapie prion, which had been present in sheep in the UK for at least 200 years. According to this theory the scrapie prion jumped species and moved into cattle when sheep offal (the leftover parts of butchered animals) was included in protein supplements fed to cattle. Other theories continue to be explored. Regardless, beginning in 1986, the UK experienced a severe outbreak of BSE, which peaked in 1992 with more than 30 000 cases.

The first case of BSE in Canada was detected in 1993, in a beef cow that had been imported from the UK in 1987. The animal was destroyed and additional measures were taken immediately by the federal government to limit the potential risk posed by previously imported cattle. The first case of BSE in an animal born and raised in Canada was found in May 2003. Since then, 10 additional cases have been identified in Canada. All of these cases have been thoroughly investigated by the Canadian Food Inspection Agency (CFIA).

The Government of Canada, through the Canadian Food Inspection Agency (CFIA) and Health Canada, has responded to the challenges presented by BSE by developing a comprehensive suite of internationally recognized, science-based measures to effectively minimize the animal and human health risk.

Key measures include:

• In 1990, making BSE a reportable disease, requiring that any suspected case of BSE be reported to a federal veterinarian.

• In 1997, banning the feeding of rendered protein products from ruminant animals (cattle, sheep, goats, bison, elk or deer) to other ruminants.

• Applying import controls to prevent the importation of high-risk animals and potentially infected animal products from other countries.

• Since 2003, requiring the removal of certain cattle tissues, known as specified risk material (SRM), from all animals slaughtered for human consumption. SRM are those tissues that, in BSE-infected cattle, are capable of transmitting BSE to susceptible species.

• Conducting BSE surveillance since 1992 to monitor cattle populations for the presence of BSE and to assess the effectiveness of BSE safeguards.

• Implementing an enhanced feed ban in 2007 to prohibit the use of SRM designated tissues in the manufacture of animal feed, pet food and fertilizer.

In May 2007, the World Organization for Animal Health officially categorized Canada as a Controlled BSE Risk country. This status recognizes the effectiveness of Canada's surveillance, mitigation and eradication measures. The science-based categorization system administered by the World Organization for Animal Health provides the framework for fair and standardized international trade based on safeguards agreed to by the 172 member countries.

The Government of Canada is working with the Canadian cattle industry, provincial governments and animal health professionals to eradicate BSE from Canada.