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

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Background

On May 8, 2009, 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 rapid test that did not rule-out BSE.

Brain samples were forwarded to the National BSE Reference Laboratory in Lethbridge, Alberta. The sample was confirmed as BSE positive using the Scrapie Associated Fibril Immunoblot and mAB 6H4 on May 14, 2009.

Additional testing included the Prionics-Check Priostrip performed on May 12, 2009, Prionics-Check Western, Hybrid Western Blot and BioRad TeSeE ELISA performed on May 13, 2009. All tests were positive. Western blot results indicate the case was c-type (classical) BSE.

The carcass was secured at the sampling site (on farm) and 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 cow born on August 26, 2002. She was 80 months of age at the time of death. The animal was born, raised and had spent her entire life on the same farm. The producer reported the duration of illness as approximately two weeks.

Retrospectively, the owner acknowledged a change in behaviour starting at the end of February, 2009 with the animal exhibiting erratic behaviour, trying to jump the gutters in the barn and falling down a few times.

The case animal became progressively more nervous around the other cows and her status in the herd changed from a dominant position to one of the lowest in the herd. She became stiff gaited in all four legs and during the last week of life she became hypersensitive to touch and reacted abnormally to visual stimuli.

Weight loss and decreased milk production were also reported. At the time of examination by the private veterinarian, she appeared weak with subtle to mild ataxia of the hind legs. 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 Northern Alberta. The feed/ birth cohort was determined to comprise 213 animals which, along with the case animal, were raised on the farm. This cohort consisted of male and female Holsteins. The trace-out investigation located 19 live animals on five premises including the case farm. These animals were quarantined and eight of the 19 live cohorts have been humanely destroyed and their carcasses disposed of by incineration in accordance with the OIE recommendations. The same approach will be followed for the remaining live cohorts.

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

  • 77 animals were traced and confirmed to have died or been slaughtered;
  • 67 animals were traced and presumed to have died or been slaughtered;
  • three animals were traced and confirmed to have been exported for slaughter and the importing country has been notified
  • 47 animals were determined to be untraceable because of records limitations

Feed Investigation

The feed investigation focussed on feeds to which the case animal may have had access during its first year of life and the manufacturing practices used to produce each of these feeds.

Investigation at the farm revealed dairy cattle to be the only commercially farmed species. Other animals present included a dog and several cats.

There was no pasture use on the farm and all forages were farm-grown and harvested using farm-owned equipment. Non-forage feed products included grain (barley) which was farm-grown or purchased, milk replacer, three different commercially prepared complete feeds and mineral and salt products in block or loose form. All products, with the exception of a commercially prepared complete lactation feed delivered in bulk, were supplied in packages (bagged or blocks) of 20 or 25 kg.

Heifer calves were initially fed colostrum, followed by milk replacer and calf starter beginning within three days of age and with no clearly defined weaning age. Feeding of the calf starter continued to approximately six months with forages and mineral and salt blocks introduced at approximately three months of age. From approximately six months of age onwards, heifers were fed forages, barley, and mineral products only. Bull calves were occasionally kept beyond two weeks of age and, if so, were fed the same way as described for the heifers.

Commercially prepared lactation feed was delivered directly into a bulk storage bin associated with the milking barn for use in preparing a total mixed ration for the lactating herd only. The storage, location, and intended use of this feed, in combination with the separate housing for heifers and lactating cows, as well as a lack of shared mixing or handling equipment, eliminated this feed from further investigation.

Feeds included in the investigation due to direct feeding were: milk replacer, calf starter, barley, mineral blocks and salt blocks. Feeds included in the investigation because exposure could not be eliminated were a small amount of loose mineral and breeder ration.

While much of the barley used was grown on farm, there were purchases for which specific source information was not available. There was also reported use of a third party mobile mix and roller mill employed to roll barley for the farm. Records of other products and how they were used in this roller mill were not available but it was reportedly used to mix grains with commercial supplements for non-ruminants at other locations. Its use cannot be eliminated as a source of potential contamination for rolled barley fed on the farm. Investigations of sources of milk replacer and salt products identified that these products were produced in specialized facilities dedicated to non-prohibited material products only, thereby ruling them out as possible sources of contamination.

Investigation at the manufacturer supplying the mineral block products identified these were produced in a facility that also produced feeds containing prohibited material. Cross-utilized equipment at the facility included equipment used to receive bulk ingredients and batch mixing equipment. Review of records associated with these points of production indicated procedures to prevent cross contamination with prohibited material were in place and documented.

The calf starter used during the period of interest was identified as manufactured at two different facilities. One facility provided 125 kg of product within the case animal's first month of life. The other facility provided 4550 kg of product within the case animal's first six months of life.

Production records for the facility manufacturing the 125 kg of calf starter were not available. One of the mixed pelleted ingredients used in this feed was manufactured in another facility which handled prohibited material but specific production records were not available.

The facility manufacturing the majority of the calf starter also manufactured two other products distributed to the farm (a loose mineral and breeder ration) which the case animal could have been exposed to. This facility also manufactured feeds containing prohibited material with shared equipment throughout all major points of manufacturing. Procedures to prevent cross contamination with prohibited material were in place and documented. Documentation failures at point of bulk ingredient receiving were noted on two occasions. Findings of the investigation suggest the most likely exposure to infectious material to be through cross-contamination of ingredients used in the manufacture of calf starter fed during the first six months of life (either manufacturer). Additional sources, particularly barley potentially contaminated by cross utilized rolling equipment, 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. 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 16 positive animals detected.

With respect to BSE, the safety of beef produced in Canada is assured by public health measures further enhanced 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. 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 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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