Bovine Spongiform Encephalopathy (BSE)
What is BSE?
BSE or "Mad Cow Disease" is a progressive, fatal disease of the nervous
system of cattle. It is what is known as a transmissible spongiform encephalopathy (TSE).
Other TSEs include scrapie in sheep, chronic wasting disease in deer and elk, and Creutzfeldt-Jakob
disease 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 in Canada
In 1993 BSE was found in a beef cow that had been imported from Britain in 1987. The
animal was destroyed and additional measures were taken immediately by the federal
government to deal with any risk that Canadian cattle might have been affected.
Canada's first case of BSE in a domestic animal was found in May 2003. This case and
all of the limited number of subsequent cases have been thoroughly investigated, with reports on the findings
made available on the CFIA web site.
BSE has been a reportable disease in Canada since 1990.
Symptoms/Signs of BSE
BSE is an unusual disease in that the time between an animals exposure to the
disease and the onset of clinical signs normally ranges from four to five 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 two to six months before the animal dies.
Transmission of BSE
Scientists believe that the spread of this disease in cattle in Great Britain was
caused by feeding protein products made from infected cattle or sheep. This occurred in
the late 1970s and early 1980s. It was then magnified by the practice of feeding rendered
material from slaughtered cattle to other cattle. The protein that is linked to BSE is
resistant to normal inactivation procedures such as heat, which means that it may not be
completely destroyed in the rendering process and could remain active in rendered
material. In 1988, Great Britain banned the use of this rendered material in animal feeds,
thus removing potentially contaminated material from the food chain. As a result, since
the winter of 1992-93, the number of BSE cases reported in Great Britain has been
progressively dropping. In addition, other possible methods of transmission are still
being scientifically investigated.
Diagnosis of BSE
There is no test to diagnose BSE in live animals, although a tentative diagnosis may be
made based on clinical signs. Diagnosis can only be confirmed by microscopic examination
of the animals brain after its death.
How Does Canada protect food safety and animal health from BSE?
Canada, as well as many other countries, has taken precautions to prevent the
introduction and spread of BSE. These measures include the following:
- The creation of a surveillance program in 1992 in which the brains of high-risk 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.
- Making BSE a reportable disease in 1990, such that any suspect case of BSE must be
reported to a federal veterinarian.
- The creation of a Canadian Cattle Identification Program in 2001 for cattle and bison,
making it possible to trace individual animal movements from the herd of origin to
slaughter.
- Controlling the importation of products that are assessed to have a high risk of
introducing BSE into Canada. Canada only allows the importation of live ruminants and
their meat and meat products from countries that Canada considers to be free of BSE.
Canada also has additional import controls for animal products and by-products from
countries that have confirmed BSE in native animals. Their animal products are assessed on
a case-by-case basis and may be permitted entry if they are judged not to present a risk
of introducing BSE.
- Canada has not imported ruminant-derived meat and bone meal for the purpose of livestock
feeding from Europe for more than a decade. In December 2000, the CFIA suspended the
importation of rendered animal material of any species from any country that Canada did
not recognize as free of BSE.
- Canada requires the removal of certain cattle tissues, know as specified risk material (SRM),
from all animals slaughtered for human consumption. SRM are tissues that, in BSE-infected
cattle, contain the agent that may transmit the disease. In diseased animals, the
infective agent is concentrated in certain tissues such as the brain and spinal cord.
Canada is continually assessing international scientific information as it becomes
available and modifying policies as required, based on new information.
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