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

BACKGROUND

On November 3, 2008, the Canadian Food Inspection Agency (CFIA) sampled a Holstein cow under Canada's National BSE Surveillance Program. Brain samples were received by the British Columbia Ministry of Agriculture and Lands (BCMAL) Laboratory, where they were screened for BSE using a Prionics rapid test. The result of this preliminary test did not rule out BSE. In accordance with the prescribed testing protocol, the test was repeated and produced a reaction a second time. Brain samples were then sent to the National BSE Reference Laboratory in Lethbridge, Alberta. Additional testing for BSE (Prionics-Check PrioStrip, BioRad TeSeE ELISA, Prionics-Check Western and Hybrid Western Blot) was conducted at the National BSE Reference Laboratory to validate the result of the screening test and was positive on Nov 6, 2008. The Scrapie Associated Fibril Immunoblot procedure was positive on Nov 7, 2008 and the immunohistochemistry procedure was positive on Nov 14, 2008. The carcass was secured at the sampling site and will subsequently be transferred to CFIA's Lethbridge laboratory 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 2008) of the World Organisation for Animal Health, referred to as 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 a registered Holstein dairy cow born on January 1, 2001, and it was 94 months of age at the time of death. The animal was born, raised and had spent its entire life on the same farm. The producer reported the duration of illness as less than 2 days with the animal exhibiting an abnormal gait (locomotion, change in movement), which was worse on the hind end. The animal had a short stunted gait and exhibited signs of ataxia (uncoordinated movements). The producer elected to have the animal humanely destroyed. Since the inclusion criteria of Canada's National BSE Surveillance Program were met, arrangements were made to forward appropriate samples for laboratory evaluation.

The birth farm was a dairy operation located in the Fraser Valley area of British Columbia. The feed cohort was determined to comprise 187 animals, which along with the case animal, were raised on the farm. This cohort consisted of female Holsteins. Males sold at less than two weeks of age for fattening and subsequent slaughter without having access to any commercially prepared feeds were excluded from the investigation because they were not exposed to the same potentially contaminated feed as the case animal. No males were retained or raised on the farm. The trace-out investigation of the feed cohort located 22 live animals on the case farm. These animals are quarantined and will be humanely destroyed; their carcasses disposed of by incineration in accordance with the OIE recommendations. The following is the disposition of the remaining animals in the feed cohort:

  • 122 animals were traced and confirmed to have died or been slaughtered;
  • 24 animals were traced and presumed to have died or been slaughtered;
  • 5 animals were traced and confirmed to have been exported for slaughter and the importing country has been notified; and
  • 14 animals were determined to be untraceable because of records limitations.

FEED INVESTIGATION

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 had access were intended for feeding to ruminants. These consisted of farm-grown and purchased forages and silages and mixed feed products provided to the farm from one commercial supplier. On-farm mixing equipment consisted of a mixer wagon used to combine forages with commercial products for calves, heifers and lactating cows. Several cats on the farm were fed in the barn and one dog was fed in the house away from the dairy operation. It is reasonable to presume that the cat and dog food did contain prohibited material; however, review of farm feeding practices confirmed that ruminants did not have access to these feeds.

For the first three weeks of life, the case animal was housed individually in a calf pen and fed milk and a commercially prepared calf ration. From 3 to 9 weeks the animal was housed in a series of group pens with animals of similar age and continued to be fed calf ration and milk as well as hay and had access to two kinds of mineral blocks. From 9 weeks to 12 months the animal continued to cycle through several group pens with animals of similar age and continued to be fed calf ration, hay and farm grown corn and grass silages as well as having access to two kinds of mineral blocks. Additionally, a dry cow mineral was added to the animal's diet at the 3 month stage.

The only other commercial feed products used on the farm included a complete ration for the lactating cows and a dry cow ration. On-farm investigation confirmed that the lactation ration was not fed to the case animal prior to twelve months of age, however, the same on-farm mixer wagon was used to mix rations for both the case animal and the lactating cows. It was also determined that the case animal could not have access to the dry cow ration which was received, stored and fed directly from bags and away from animals less than one year of age.

Investigation at the commercial feed manufacturer, which was the sole supplier of calf ration and lactation ration, identified that this facility handled prohibited material. Components of this facility were dedicated to the manufacture of feeds not containing prohibited material in the formula. However, bulk ingredient receiving and finished feed conveyances were cross-utilized. Written procedures and production records were insufficient to rule out possible contamination with prohibited material at these points affecting both ration types delivered to the case farm.

Investigation at the commercial feed supplier identified that the two kinds of mineral blocks were manufactured by a separate facility, independent of the main commercial feed manufacturer. Investigation at the manufacturer of these blocks determined that this facility did handle prohibited material during the period of interest; however, no written procedures or production records were available. As the period of interest occurs after the introduction of the 1997 Mammalian Feed Ban, it is unlikely that ruminant meat and bone meal was intentionally used in the formulation of either of these mineral blocks. However, as production records are not available for review, it is not possible to rule out the possibility that contamination during production could have taken place.

The dry cow mineral used on farm was obtained from a specialized facility not handling prohibited material and was packaged in bags. This product was ruled out as a possible source of contamination.

Considering the farm's feeding regime and specific production records reviewed, a likely source of exposure to BSE infectivity appears to be potentially contaminated heifer ration. However, the risk associated with possible ingestion of small amounts of the lactation ration and either of the mineral blocks exists, and potential contamination of these products cannot be ruled out.

INVESTIGATION OVERVIEW

The detection of this case does not change any of Canada's 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 (including non-ambulatory animals). This effort is directed at determining the level of BSE in Canada, while monitoring the effectiveness of the risk-mitigating measures in place. Canada's National BSE Surveillance Program continues to demonstrate an extremely low level of BSE in Canada, with 15 positive animals detected.

With respect to BSE, the safety of beef produced in Canada is assured by public health measures enacted in 2003. The removal of specific 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 is effectively preventing the amplification of BSE in Canada's feed system. Additional regulations to enhance Canada's feed ban were enacted in 2007. The most important change is 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 per cent 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.