REPORT ON THE INVESTIGATION OF THE EIGHTH CASE OF BOVINE SPONGIFORM ENCEPHALOPATHY (BSE) IN CANADA

Background

On August 9, 2006, a commercial beef cow on a farm in northern Alberta died following a short history of neurological disease. The following day a private practitioner sampled the cow under Canada's National BSE Surveillance Program. Brain samples from this animal were sent to the Alberta Agriculture, Food and Rural Development (AAFRD) Laboratory, where they were screened for BSE using a Bio-Rad rapid test. The preliminary test results received on August 16, 2006 did not rule out BSE. In accordance with the prescribed testing protocol the test was repeated on August 17 and produced a second reaction.

Brain samples were then sent to the National Centre for Foreign Animal Disease in Winnipeg where rapid screening tests were performed, validating the work of the AAFRD, and BSE was confirmed by the Scrapie Associated Fibril immunoblot and MAB monoclonal antibody 6H4 procedure on August 23, 2006. This method had been chosen because of poor tissue quality (autolysis and freezing artefact) which prevented a definitive identification of target areas for immunohistochemistry. The carcass was secured from the farm, transferred to the AAFRD laboratory and incinerated. No part of the carcass entered the human food supply or animal feed chain.

The CFIA immediately initiated an epidemiological investigation based on the most recent World Organization for Animal Health (OIE) recommended BSE guidelines. Specifically, the CFIA investigated:

• The birth cohort (all cattle born in the same herd as, and within 12 months of the birth of the BSE-positive animal);
• the feed cohort (all cattle which, during their first year of life, were reared with the BSE positive animal during its first year of life, and which investigation showed consumed the same potentially contaminated feed during the period); and
• feed to which the animal may have been exposed early in its life.

Animal Investigation

The positive cow was a Charolais crossbred cow estimated as approximately eight to ten years of age at the time of death by examination of her dentition. The herd on the index premises had been assembled since 2001, including the purchase of the index case. The positive cow was therefore purchased within the previous five years and was not born at the index premises. The producer reported the duration of illness was more than one week, during which the animal exhibited neurological signs including ataxia and tremors and became non-ambulatory (downer). The producer treated the animal for milk fever, but despite treatment, she died. The following day a private practitioner attended the premises to perform a post-mortem examination which revealed the likely cause of death was peritonitis. Because the animal met the inclusion criteria of Canada's National BSE Surveillance Program, arrangements were made to forward appropriate samples for laboratory evaluation.

The index farm was a commercial cow-calf operation. The index animal was a purchased addition and there was no evidence that any members of its birth or feed cohort were also present on the index premises. The investigation initially focused on the determination of the farm of origin (birth farm) of the positive cow. Because the positive cow was not uniquely identified within the herd, and the farm's purchase records did not conclusively document a specific transaction for the acquisition of this particular cow, all purchases made by the producer since the inception of the herd in 2001 were investigated. It is possible that the cow was acquired before the introduction of the first phase of regulations requiring official identification of individual animals at the time of their movement (July 2001) or before enforcement of the regulations was implemented. There would have been no requirement for subsequent application of official identification to the cow, as it had not been moved from its farm of residence since.

Of 56 possible sources of the farm of origin of the positive cow that were investigated, 43 were definitively ruled out based on the profile of the index cow (estimated age, color, breed-type, sex) and the potential source farms' management practices (age of cows sold, colour, breed-type, producers' application of man-made identification). Information provided by the Livestock Identification Services Ltd. in Alberta and the Canadian Cattle Identification Agency (CCIA) was integral to the investigation. Because it was impossible to distinguish among the 13 remaining possible sources of the index cow, the animal was determined to be untraceable and no further action could be undertaken with respect to the birth or feed cohort, or the feed investigation.

The CFIA's previous experience with trace out investigations of birth and feed cohorts would suggest that for a cow of this age (eight to ten years), over 90% of its birth or feed cohort would have previously left the cattle population due to attrition.

Feed Investigation

BSE feed investigations focus on the critical period of susceptibility to BSE during the first year of life of positive animals and encompass all potential avenues of direct exposure to prohibited material as well as potential areas of cross-contamination. Because the birth farm of this animal could not be definitively determined, no feed investigation could be conducted. It has previously been demonstrated that the BSE agent was present on limited occasions in the Northern Alberta area during the period (1996-1998) spanning the estimated first year of this animal's life and its maximum susceptibility period. This period also coincides with the introduction of regulations to prohibit the feeding of mammalian protein to ruminants in Canada. The animal would have been born and exposed before the feed ban came into effect or during the early stages of implementation. At that time feed containing prohibited material may have remained on farms and feed mills which were adapting to the new requirements.

The possibility that the exposure occurred on the index premises where the positive animal lived since approximately 2001 was ruled out based on the very limited susceptibility of older animals.

Investigation Overview

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 (including animals which die on-farm). This effort is directed at determining the level of BSE in Canada, while monitoring the effectiveness of the suite of risk-mitigating measures in place. Canada's National BSE Surveillance Program continues to demonstrate an extremely low level of BSE in Canada, with eight positive animals detected among over 128,000 targeted tests conducted since 2004. Such detections demonstrate the effectiveness and integrity of Canada's surveillance system; the level of awareness existing at all levels of the animal and meat production systems; the value of financial reimbursement provided for sampling and carcass disposal; and the commitment of Canadian producers and veterinarians to eliminating this disease. Canada's surveillance program adheres to OIE guidelines.

Other Relevant Information

Canada remains committed to the achievement of high standards of animal and public health protection and food safety. As neither science nor international standards are static, continuous assessment and adjustments are undertaken to reflect new knowledge, technology or approaches.

Amendments to the Health of Animals Regulations to enhance the Canadian Cattle Identification system instituted in July 2001 were made June 14, 2005. These amendments removed exemptions from the requirement to tag animals. The requirement to identify was extended to dead stock and the requirement to report information on identified dead stock was expanded to include producers disposing of dead stock on their own premises.

To facilitate traceability, tag distributors were required to report producer information to the national database within 24 hours. Individuals were required to report the correlated numbers when applying a new tag to an animal that was already identified and it was no longer permitted to replace an approved tag with another tag for animals destined for the export market.

On September 1, 2006, the CCIA further enhanced the Canadian Cattle Identification Program. CCIA's Policy now requires Radio-Frequency Identification (RFID) tags on all cattle leaving their herds of origin. This will facilitate Canada's tracing of movements and electronic recording of identification at additional levels in the animal production chain.

The safety of beef produced in Canada is assured by public health measures enacted in 2003, following the first detection of BSE in a native-born animal in Canada. The removal of Specified Risk Materials (SRM), those tissues which 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.

International experts agreed that the proactive implementation of the 1997 mammalian to ruminant feed ban in Canada was a critically important factor in limiting the spread and preventing the amplification of BSE in the feed system. In independent reviews in 2005 the United States Department of Agriculture and the Canadian Food Inspection Agency concluded that the ban, as designed, implemented and currently applied, provides an effective barrier that is contributing to reducing the risk of BSE.

Regulations to enhance Canada's feed ban were announced on June 26, 2006. The most important change will require the removal of specified risk material from all animal feeds, pet food and fertilizer. The enhancement will significantly accelerate progress toward eradicating BSE from the national cattle herd by preventing more than 99% of potential BSE infectivity from entering the Canadian feed system and eliminating opportunities for cross-contamination within the complex system of production, transportation and storage of animal feeds. For further information, please see the fact sheet, "Canada's Enhanced Feed Ban", at http://www.inspection.gc.ca/english/anima/feebet/rumin/enhrene.shtml.

Footnote:
Based on revisions to the Bovine Spongiform Encephalopathy Chapter of the OIE Terrestrial Animal Health Code (2006), the CFIA amended its policy regarding the destruction of calves of BSE positive cows born within 24 months of the development of clinical signs. Since August 2006, CFIA no longer requires their destruction for disease control. However, the CFIA will continue to trace calves born to a positive female in respect of current export certification requirements requested by some importing countries.