ARCHIVED - Report on the Investigation of the Eighteenth Case of Bovine Spongiform Encephalopathy (BSE) in Canada

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Background

On February 10, 2011, the Alberta Provincial Laboratory informed the Canadian Food Inspection Agency (CFIA) Edmonton District Office of a BSE Surveillance sample (collected through the Canada Alberta BSE Surveillance Program) with a reaction on the BIO-RAD TeSeE ELISA rapid test that did not rule-out BSE.

Samples were forwarded to the National and OIE (World Organisation for Animal Health) BSE Reference Laboratory in Lethbridge, Alberta. The samples were reported as BSE positive using the immunohistochemistry (IHC) procedure on February 18, 2011. In addition to the IHC procedure, the National BSE Reference Laboratory evaluated the sample using the Prionics-Check Western® rapid test, Hybrid Western Blot, the Prionics Check PrioSTRIP® rapid test, BioRad TeSeE ELISA and the Scrapie Associated Fibril Immunoblot (SAF immunoblot). All test results were determined to be positive. Western blot results indicate the case was C-type (classical) BSE.

The carcass was secured at the sampling site and transferred to CFIA's laboratory in Lethbridge for incineration. No part of the carcass entered the human food supply or animal feed chain.

The CFIA immediately initiated an epidemiological investigation based on the recommended BSE guidelines (Terrestrial Animal Health Code 2010) of the OIE. Specifically, the CFIA followed the recommended BSE guidelines for a country with controlled risk status and investigated:

  • the feed cohort, comprising all cattle which, during their first year of life, were reared with the BSE case during its first year of life, and which investigation showed consumed the same potentially contaminated feed during that period, or
  • the birth cohort, comprising all cattle born in the same herd as, and within 12 months of the birth of the BSE case, if the above cannot be identified and
  • feed to which the animal may have been exposed early in its life.

Animal Investigation

The positive animal was confirmed to be a purebred Holstein dairy cow born on August 23, 2004, therefore 77 months of age at the time of death. The animal was born, raised and had spent its entire life on its birth farm. The positive animal exhibited neurological signs for three weeks before the producer contacted the private veterinarian. It was ataxic, had a head tilt, difficulty getting up and would circle once it was up. After consultation between the producer and the local veterinary practitioner it was determined that the animal met the inclusion criteria of Canada's National BSE Surveillance Program. The animal was euthanised on February 04, 2011 and arrangements were made to collect and submit appropriate samples for evaluation.

The birth farm is a large corporate farming operation. Aside from the dairy herd, they also had poultry, beef cattle and sheep during the period of interest which was determined to be August 23, 2003- August 23, 2005. However, each herd or flock belonging to this operation was managed as a distinct unit under its own manager. The beef herd and sheep flock did not commingle with the dairy herd or with each other and were fed different rations.

The birth and feed cohort was determined to comprise 361 animals. The trace-out investigation located 21 live animals on 3 premises including the birth farm. All of these animals have been placed under quarantine. To date, 2 of the 21 live cohorts have been humanely destroyed and the carcasses have been disposed of at an SRM approved landfill in accordance with OIE recommendations. The remaining cohorts are permanently identified, are under official movement control, and will be destroyed or, upon their death, their carcasses disposed of in accordance with OIE recommendations.

The following is the disposition of the other animals in the birth/feed cohort:

  • 138 animals were traced and confirmed to have died or been slaughtered;
  • 128 animals were traced and presumed to have died or been slaughtered;
  • 38 animals were traced and confirmed to have been exported for slaughter and the importing country has been notified
  • 36 animals were determined to be untraceable because of records limitations

Feed Investigation

The purpose of the feed investigation is to identify possible sources of exposure of the case animal to "prohibited material", animal byproducts defined in Canada's Health of Animals Regulations that are prohibited from being fed to ruminant animal species due to their risk of transmitting BSE. The feed investigation focused on feeds to which the case animal may have had access during its first year of life and on the manufacturing practices used to produce these feeds. All feed products to which the BSE case animal was known to have had access were intended for feeding to ruminants.

Feeding Practices

Male and female calves were housed in calf hutches for the first four weeks of life. They were fed cow's milk for the first week, and then cow's milk supplemented with a commercially prepared calf starter. Between one and four weeks of age, male calves were sold to a calf feeder while the female calves remained in the hutches and were provided with the same diet until eight weeks of age.

At eight weeks of age, the remaining calves were relocated to pens containing 16-20 calves in each, and from eight weeks until twenty weeks of age they would have had access to commercial calf starter ration, hay and salt.

From twenty weeks until one year of age, the calves were housed in larger pens with 35-40 calves in each and were fed a total mixed ration (TMR) containing silage, barley, heifer mineral, straw, and either canola meal, soymeal or dried distiller's grains. They also had access to hay and a free-choice heifer mineral during this time. The dairy animals had no access to other commercial feeds used on the farm.

The Investigation revealed that the truck used to transport grains on farm was also used to pick up poultry feeds containing prohibited material from the commercial supplier. These grains included oats destined for use in sheep rations, and barley which was subsequently used in dairy and beef rations. Interviews of farm staff indicate that the truck was physically cleaned between each use, however, the lack of written procedures and records does not allow for the ruling out of the truck as a possible point of cross contamination of grains used in dairy cattle rations with prohibited material.

Feed & Ingredient Sources

Canola and soy meals were usually received from a specialized oilseed processing facility which never handled or used prohibited material. Therefore these products were ruled out as a possible source of contamination. There was one purchase of soy meal from a commercial feed supplier which did handle prohibited material, however review of production records at the facility showed that appropriate control measures were taken, allowing this load of soy meal to be ruled out as a possible source of contamination.

The dried distiller's grains which were used on farm could not be traced back to their source. However, this product would most likely have originated from a specialized single ingredient feed manufacturing facility and would be an extremely unlikely source of contamination.

The calf starter ration, minerals and supplements used by the dairy operation were all provided by a sole commercial feed supplier, different from the supplier of feed to the poultry operation. It was confirmed through inspection reports on file that this facility had not used or handled prohibited material since at least 1997.Therefore these products were ruled out as a possible source of contamination.

The salt blocks used by the dairy operation were purchased at a retailer and confirmed as being sourced from a specialized salt manufacturer. They were therefore ruled out as a possible source of contamination.

Considering the farm's feeding regime and specific production records reviewed, the most likely source of exposure to BSE infectivity appears to be cross-contamination with poultry feed containing prohibited material resulting from incomplete clean out of a conveyance used to also deliver barley to the dairy herd.

Investigation Overview

The detection of this case does not change any of Canada's identified BSE risk parameters. The location and age of the animal are consistent with previous cases. Surveillance results to date, including this case, reflect an extremely low level of BSE in Canada.

Since the confirmation of BSE in a native-born animal in May 2003, Canada has significantly increased its targeted testing of cattle in high-risk categories advocated by the OIE. This effort is directed at determining the level of BSE in Canada while monitoring the effectiveness of the risk-mitigating measures in place.

With respect to BSE, the safety of beef produced in Canada is assured by public health measures further enhanced in 2003. The removal of specified risk material (SRM) - the tissues that have been demonstrated to have the potential to harbour BSE infectivity - from all animals slaughtered for human consumption is the most effective single measure to protect consumers in Canada and importing countries from exposure to BSE infectivity in meat products.

As demonstrated by the surveillance system, the feed ban implemented in 1997 has effectively prevented the amplification of BSE in Canada. Additional regulations to enhance Canada's feed ban were enacted in 2007. The most important change was the removal of SRM from all animal feeds, pet food and fertilizer. The enhancement will accelerate progress toward eradicating BSE from the national cattle herd by preventing more than 99 percent of potential BSE infectivity from entering the Canadian feed system. These measures are effectively minimizing the risk of BSE transmission.

Canada is officially categorized under the OIE's science-based system as a controlled BSE risk country. This status clearly recognizes the effectiveness of Canada's surveillance, mitigation and eradication measures, and acknowledges the work done by all levels of government, the cattle industry, veterinarians and ranchers to effectively manage and eventually eradicate BSE in Canada.

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