Bovine Spongiform Encephalopathy (BSE) is a progressive, fatal disease of the nervous system of cattle. It is one member of a family of diseases known as transmissible spongiform encephalopathies (TSEs). Other TSEs include scrapie in sheep, Chronic Wasting Disease (CWD) in deer and elk, and Creutzfeldt-Jakob disease (CJD) in humans.
Atypical Bovine Spongiform Encephalopathy
The form of BSE that we are most familiar with is related to the feeding of BSE-infected meat-and-bone meal (MBM) to cattle. However, occasionally a case of BSE is found that is not related to feeding MBM. The prion isolated from these cases differs from the usual form at the molecular level. These atypical BSE cases are thought to occur naturally and spontaneously and tend to occur in older animals as compared to feed-related BSE which tends to occur in 4- to 6-year-old cattle.
Causes and symptoms
Although the exact cause of BSE is unknown, it is associated with the presence of an abnormal or mis-folded form of the cellular prion protein (PrPc), which is found on the surface of cells in the central nervous system and some other body tissues. Prions are extremely resistant to heat, ultraviolet light, common disinfectants and many other methods that normally inactivate disease-causing organisms such as viruses and bacteria.
BSE is a slow developing disease. Signs of the disease may not show up for three to six years after the animal has been exposed to the BSE prion(s). Symptoms can vary between animals, and may include nervous or aggressive behaviour, abnormal posture, lack of co-ordination, lameness 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.
The Canadian Food Inspection Agency (CFIA) considers a BSE suspect to be cattle over 24 months of age showing at least three of the following signs:
- lack of coordination or difficulty while turning or rising from a lying position;
- increased sensitivity to touch, sounds or light;
- nervous, aggressive or apprehensive behaviour;
- abnormal head position;
- hesitation at doors, gates or barriers; or
- loss of body weight, condition and reduced milk production, despite continued appetite.
Bovine Spongiform Encephalopathy prion in cattle
BSE prions have been found in the brain, spinal cord and eyes of cattle infected with BSE under field conditions. In experimental conditions, prions have been found in the brain, trigeminal ganglia, tonsils, spinal cord, dorsal root ganglion, and parts of the small intestine. These materials are referred to as "specified risk material" (SRM) and are not permitted to be present in human (since 2003) or animal (since 2007) food in Canada. In additions, SRMs are subject to specific handling and disposal measures. More information on SRMs can be found on the Canadian Food Inspection Agency website.
BSE is not a contagious disease. That is, it cannot be directly spread from animal to animal. BSE prions are not present in milk or dairy products. Research indicates that the only means of spreading BSE is through the feeding of BSE-infected MBM made from BSE-infected cattle, a practice that has been banned in Canada since 1997.
Although not scientifically proven, there is strong epidemiologic and laboratory data linking a rare, degenerative, fatal brain disorder in humans called variant Creutzfeldt-Jakob Disease (vCJD) to the consumption of BSE-contaminated products.
In Canada, two rapid BSE screening tests are used for routine surveillance in dead animals: the Prionics®-Check PrioStrip and the Bio-Rad TeSeE® ELISA. When these rapid tests are used, any positive test is sent for confirmatory testing at CFIA's National and International Reference Laboratory for BSE.
Cattle producers play a key role in this surveillance program since they monitor the health of their herds and can spot any animals that should be tested. While submission of cattle for BSE testing is voluntary, producers have a responsibility to protect their industry by participating in Canada's BSE testing program. Without this participation, the program cannot succeed and without a robust BSE surveillance program trade with other countries may be compromised which could put the Canadian cattle industry in jeopardy.
Canada's minimum annual BSE surveillance target is 30,000 tests. Each province is assigned a number of tests based on the cattle population in the province. Saskatchewan producers are required to test approximately 7,500 animals each year. With the second-highest cattle herd population in the country, Saskatchewan sample numbers are of paramount importance.
Producers are encouraged to continue to participate in the National BSE Surveillance Program by continuing to submit samples from eligible cattle.
Steps for submitting samples for BSE testing
Step 1: Ensure that the animal is over 30 months old and dead, down, chronically ill (diseased) or unfit for transport. There is no test to diagnose BSE in live animals.
Step 2: Contact your local veterinarian or CFIA district office. Call 1-877-727-5273 to find out the number of your local CFIA district office. CFIA does not charge, but sample collection is limited to regular working hours. Private veterinarians will charge for sampling and are reimbursed $100 by the National BSE program. Alternately you may remove the head and take it to your veterinarian for sampling. Contact your vet for more information.
Step 3: Whoever you choose to take the sample will request information on the animal's history and basic farm information. They will also arrange a time to collect a sample at your farm.
Step 4: Upon arrival at your farm, a history of any illness, animal identification and age will be requested.
Step 5: You will be asked to sign a contract stating that you agree to control the carcass until test results are received. In return, for every eligible sample, you will receive $75.
Step 6: The veterinary clinic or CFIA inspector will remove the animal's head and collect the obex (part of the brain) through the opening in the back of the skull.
Step 7: The sample is sent to a lab for testing.
Step 8: Within two weeks, you should be contacted with the test results.
Step 9: If results are negative, no further action is required and the animal carcass no longer has to be controlled.
What happens when a case of BSE is found
When an animal tests positive for BSE, the carcass of the positive animal will be collected by the CFIA for further sampling and destruction. A detailed history of the animal will be collected to identify where it was born and what feed it was exposed to in its first year of life. Other animals from the herd born a year before and after the positive animal and fed the same feed supplement in the first year of life will be traced, quarantined and destroyed with compensation at market value. It is important to note that your entire herd will NOT be depopulated.
Investigation of the infected animal's background and identifying any animals that may have been exposed to the same source of contamination as the BSE-infected animal will be carried out. The purpose of the investigation is to:
- identify the birth farm and other farms on which the infected animal lived;
- examine feed the animal may have eaten during its first year of life;
- locate all cattle born 12 months before and after the birth of the BSE-infected animal on the birth farm; and
- locate all cattle that may have consumed the same feed as the BSE-infected animal during its first year of life.
Other response actions that will occur include:
- Quarantine all animals that may have been exposed to the same source of contamination as the BSE-infected animal, as well as the last two calves of that animal. Quarantine of these calves is done in order to meet export certificate requirements of trading partners. Quarantines may also be applied to feed that is potentially contaminated with BSE. No other restrictions are placed on the movement of animals, animal semen, embryos, or milk from the farm.
- Depopulation ONLY of animals that may have been exposed to the same source of contamination as the BSE-infected animal. In certain cases, such as maintaining animals for genetic purposes, destruction may be delayed. In these situations, animals must remain under quarantine until their ultimate destruction and disposal. Compensation is paid for animals destroyed.
- Disposal of carcasses and all potentially contaminated feed by incineration or deep burial in an authorized landfill. On-farm burial is also possible but must comply with provincial and municipal waste management requirements.
Importance of continued testing
BSE surveillance is critical for allowing Canada to improve or maintain its BSE status with the World Organization for Animal Health and the international community. Currently, Canada's BSE risk status is "controlled"; that is, BSE has been detected but adequate control and prevention measures such as surveillance, reporting and education programs and feed bans are in place. Without adequate surveillance Canada's BSE status may be lowered to "undetermined," which may reduce the number of international markets for Canadian cattle and beef products.
Continued surveillance is also required if Canada is ever to improve from the current "controlled" risk status to "negligible" risk status. "Negligible" risk status has all the same requirements as "controlled" risk status, plus the distinction of no BSE cases occurring within at least 11 years after the latest birth date of any BSE case. To date, BSE has not been found in any Canadian cattle born after 2009; if no BSE cases are found in animals born after 2009, Canada will be eligible to apply for "negligible" risk status after 2020.
To have an animal sampled for BSE, producers can either contact their private veterinarian or their local CFIA district office.
History of BSE in Canada
The first case was found in 1993, in a purebred beef cow imported from Great Britain in 1987. There have been 19 BSE cases identified in Canadian-born cattle. Eighteen of these cases were found in Canada while one case was found in the United States in a dairy cow that originated from a farm in Alberta. The most recent case was found in a cow in Alberta in February 2015.
Steps Towards Eradication of BSE in Canada
Over the years, Canada has implemented a number of precautions to prevent the spread of BSE and to eventually eliminate it from the Canadian cattle herd. These measures also protect public health.
1990 - BSE becomes a reportable disease. Any suspect cases of BSE must be reported to the CFIA, which is responsible for control and eradication of the disease, under the authority of the Health of Animals Act.
1997 - Introduction of a ruminant-to-ruminant feed ban, meaning that rendered protein products from ruminant animals (cattle, sheep, goats, bison, elk or deer) cannot be fed to other ruminants.
2000 - Ban of the import of rendered animal material from any species from any country that Canada does not recognize as free of BSE.
2001 - Canadian Cattle Identification Agency- traceability program established to assure efficient trace back and containment of serious animal health and food safety concerns in the Canadian cattle herd, including BSE.
2003 - Removal of SRM from the human food chain.
2007 - The Enhanced Feed Ban came into effect. These changes are designed to provide additional controls against BSE by addressing the risks associated with cattle being exposed to SRM in feeds made for other animals.
In addition to the above measures, the CFIA implemented a BSE surveillance program in 1992 in which the brains of high-risk cattle showing signs consistent with BSE were tested for the disease. Enhanced active surveillance, beginning in 2004, targeted animals over 30 months of age that are dead, down, dying and diseased. The surveillance program continues to be a critical part of the efforts to control BSE in Canada.
Other Countries with BSE
BSE has been detected in at least 27 countries other than Canada. The majority of cases have occurred in Europe. A full list of countries affected and number of cases can be found on the World Organisation for Animal Health website.