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REPORT ON THE INVESTIGATION OF THE FOURTH CASE OF BOVINE SPONGIFORM ENCEPHALOPATHY (BSE) IN ALBERTA, CANADA

Background

On January 12, 2006 a private veterinarian in North Central Alberta euthanized and sampled a Holstein-Hereford cross bred cow under Canada's National BSE Surveillance Program. Brain samples from this animal were sent to an Alberta provincial laboratory where they were screened for BSE using a Bio-Rad rapid test. The sample produced an inconclusive reaction on January 17, 2006. In accordance with the prescribed testing protocol, the test was repeated and on January 18 produced a reaction a second time. Brain samples were then sent to the National BSE Reference Laboratory at the Canadian Science Centre for Human and Animal Health in Winnipeg where BSE was confirmed using the immunohistochemistry procedure on January 22, 2006. No part of the cow entered the human food or animal feed chain. The carcass was secured from the index premises and transferred to the Canadian Food Inspection Agency (CFIA) Lethbridge laboratory where it was subsequently incinerated.

The CFIA immediately initiated an epidemiological investigation along three lines of enquiry, based on the World Organization for Animal Health (OIE) BSE guidelines, namely:

• calves born to the affected cow during the two years prior to the onset of clinical signs;
• the birth and feed cohort (cattle born on the farm of origin within the twelve months before and the twelve months after the birth of the affected animal or animals purchased and present on the farm during this period which were also in their first year of life); and
• feed to which the animal may have been exposed early in its life.

Animal Investigation

The affected Holstein-Hereford cross cow was born on April 15, 2000 and therefore was 69 months or just under six years old at the time of death. The animal lived her entire life on the farm of birth. The affected cow had a history of not performing well for at least the past month. When examined on January 12, 2006 the animal exhibited abnormal locomotion and posture. The practitioner and producer determined that the animal should be euthanized, and because it met the criteria of Canada's National BSE Surveillance Program, samples were forwarded for laboratory analysis.

The investigation revealed that the affected cow had two calves during the two years prior to the onset of clinical signs. The 2005 offspring was located on the farm of origin. It was transported to the CFIA Laboratory in Lethbridge, where it was euthanized, sampled and tested negative for BSE. The carcass was incinerated.

The 2004 offspring had been sold in a lot of 14 cattle to another producer, and was determined to have died during its first year of life on the second premises.

Its carcass did not leave the premises.

The index premises comprised a dairy herd and a cow-calf beef operation. The birth and feed cohort was determined to comprise 156 animals which, along with the affected animal, were born on the index premises in the dairy operation. The cohort included purebred Holsteins destined for the dairy herd or for sale and cross bred offspring removed to the beef herd at approximately one year of age or sold at an earlier age. The trace-out investigation of the birth and feed cohort located 38 live animals on the index premises and in other herds to which they had been sold. These animals were subsequently euthanized, sampled and tested negative for BSE. Because the birth cohort cattle would now be five to seven years of age, most had previously been slaughtered or died of natural causes. The disposition of the remaining 118 animals in the cohort was determined to be:

• 27 animals had died on the farm of origin
• 90 animals were traced and determined to have died or been slaughtered at other locations
• One animal was traced and confirmed to have died and been tested under Canada's National BSE Surveillance Program with negative results.

Feed Investigation

A thorough and detailed feed investigation was conducted at the farm of origin to identify all of the feed materials used, the suppliers and sources of these products, and the feeding and feed storage management practices. The on-farm investigation focused on potential cross contamination or incidental exposure to feeds that could have contained prohibited ruminant feed ingredients.

Investigations were conducted at all identified feed suppliers and included identifying use of, or potential contamination with, material prohibited from feeding to ruminants. Specific attention was directed to ingredient sourcing, transportation, handling, manufacturing, storage and delivery practices.

Results of the investigation on the farm revealed that the index animal had direct exposure to four different commercial products representing two different suppliers during the first year of life and a further four different commercial products from the same two suppliers at approximately 12 to 14 months of age.

None of the product formulations contained material prohibited from use in ruminant feeds. One of the two suppliers produced feeds for ruminants as well as feeds for non-ruminant species. The feeds produced for non-ruminant species included material prohibited for use in ruminant feeds. This manufacturing facility had procedures in place to minimize opportunities for contamination of ruminant feeds with prohibited material and comply with the regulatory requirements of the feed ban.

A detailed review of individually manufactured products from this facility and to which the index animal was or was potentially exposed, identified incidents of concern where ruminant feed was processed or transported immediately following the processing of a feed for non-ruminant species containing prohibited material. Documentation did not always demonstrate that proper clean out of cross-utilized equipment had occurred.

Forages used on the farm were grown and harvested on the farm or occasionally purchased from neighbours and transported with farm owned equipment. The only on-farm mixing equipment was a feed wagon used to combine forages with commercially prepared rations for the lactating dairy herd. This equipment was never shared or loaned off the farm. The use of commercial feed products was limited to those intended for ruminants and a bagged pet food product for dogs that was stored in the garage and fed at the house. Bin management practices on the farm extensively minimized but did not completely eliminate the possibility that feed products produced prior to the ban were present to some extent on the farm, three years subsequent to the ban.

Investigation Overview

Given current knowledge about the epidemiology of BSE, it is reasonable to presume that this animal was exposed to feed containing a low level of infectivity during its first year of life. The investigation into the current case identified a number of possibilities but it was impossible to determine the exact source of exposure with a high degree of certainty. However, the findings indicate that a particular calf grower ration could have become contaminated during either manufacture or distribution. Furthermore, investigators could not rule out the somewhat remote possibility of residual pre feed ban materials persisting on the farm.

It is uncertain if such contamination is attributable to a remnant of the low level of infectivity previously demonstrated to be circulating in the feed system in this geographical area or a more contemporary occurrence.

For an analysis of the temporal and spatial distribution of BSE in North America, refer to Canada's Assessment of the North American BSE Cases Diagnosed From 2003 to 2005 - Part II published February 2006. It is available at: www.inspection.gc.ca/english/anima/heasan/disemala/bseesb'eval2005/evale.shtml

The detection of BSE affected animals born after the introduction of a feed ban is not unique to Canada, and does not indicate a failure of the measures in place to reduce and eventually eradicate BSE. In other countries that have experienced cases of BSE, similar events have occurred. While measures equivalent to Canada's feed ban have been demonstrated to curtail the amplification and spread of BSE in cattle and would lead to the elimination of the disease over time, additional measures to further reduce any potential for cross-contamination would hasten eradication.

The safety of meat currently being produced in Canada is assured by public health measures enacted in 2003, following the first detection of BSE in Canada. The removal of specified risk materials (SRM) from all animals slaughtered for human consumption in Canada is the most effective single measure to protect consumers in Canada and importing countries from exposure to BSE infectivity in meat products.

While this fourth case of BSE is unwelcome, it is not unexpected. The first case, detected in May 2003, indicated that Canada had a low, previously undetected level of BSE. Therefore increased testing of animals from high risk categories, as was this case, an animal exhibiting signs neurological abnormality, was intended to determine the prevalence of BSE in Canada, and to monitor the effectiveness of the suite of mitigating measures in place. It is reassuring that, among over 88,000 targeted tests conducted since 2003, this is only the fourth positive animal detected, indicating an extremely low prevalence of BSE in Canada. Such detections also demonstrate the integrity of Canada's surveillance system and the commitment of Canadian producers and veterinarians to contributing to the elimination of this disease in Canada.

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