Animals > Animal Diseases > Bovine Spongiform Encephalopathy > Case 6 - Manitoba 2006 

Report on the Investigation of the sixth case of Bovine Spongiform Encephalopathy (BSE) in Canada

(Province of Manitoba)

August 8 , 2006

Background

On June 15, 2006, a commercial beef producer in Manitoba euthanized a diseased Charolais cross bred cow. Tissue samples were collected by the producer’s private veterinarian for testing under the National BSE Surveillance Program.

The sample was received by the Manitoba provincial laboratory on June 22, 2006 where it was screened for BSE using a rapid BSE test (BioRad ELISA). The preliminary test results received on June 29, 2006 did not rule out BSE. Therefore, in accordance with standard operating procedures, the test was repeated on June 30, 2006 using the original and re-cut tissues which produced identical results.

Staff of the National BSE Reference Laboratory (BSE-RL) collected the brain for confirmatory testing at the Canadian Science Centre for Human and Animal Health in Winnipeg. On June 30, additional positive rapid screening test results were generated using the Prionics-Check Priostrip and Prionics-Check Western Blot and BSE was confirmed on July 3, 2006 using the immunohistochemistry procedure. At the same time, the Hybrid Western Blot test was performed and differences in immunobiochemical patterns including the apparent molecular weight of PrPres protein, glycoform distribution, and detection using P4 monoclonal antibody, confirmed this case as BSE with a phenotype consistent with a less prevalent strain of BSE previously reported in Europe and the US.

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

• calves born to the affected cow during the two years before the onset of clinical signs;
• the birth and feed cohort (cattle born on the farm of origin within 12 months period before and after the birth of the affected animal or animals purchased and present on the farm during these periods, which were also in their first year of life and subject to the same feed); and,
• feed to which the animal may have been exposed early in its life.

Animal Investigation

When the positive BSE sample was collected, a second BSE surveillance sample was taken from another cow on the same premises. To ensure sample integrity and the identification of the remainder of the carcass, DNA analysis was performed on both samples and their associated animal parts. DNA results confirmed the submission as originally submitted and the identity of the hide.

The affected cow was determined to be 16 or 17 years old at the time of destruction, based on the owner’s records. The age of the animal limited the investigation as the time period exceeded normal information retention including written records (auction records are kept for seven years) and human memory.

The affected cow had deteriorated in the week before its death and had become non-ambulatory. Based on the poor prognosis for this animal, the producer decided that the animal should be destroyed and, because it met the criteria of Canada's National BSE Surveillance Program, a private veterinarian was called to collect samples for laboratory analysis.

The index premises is a beef cow-calf operation with approximately 125 head on site. The producer retains some replacement heifers from their stock and purchases heifers. The producer also buys older cull cows and maintains them in a non-traditional production unit. The BSE-infected cow was an aged animal that had been purchased by the index farm in January 1992 as a bred heifer. The farm records indicated that she had her first calf in the spring of 1992. Therefore, the cow was either two or three years old in 1992 and was born in 1989 or 1990. This cow was originally purchased in 1992 from local cattle dealers as part of an assembled group of heifers. Confirmation that the cow was part of the 1992 shipment is based on: her dentition at the time of euthanasia, which was consistent with an aged cow; the finding of a unique dealer’s brand on the hide; and, supporting farm records and tags. Tracing the birth farm was attempted, but proved not to be possible because the required records were not retained. The animal date of birth predates the mandatory animal identification program initiated in 2001.

The CFIA investigation could not exclude other cows as birth or feed cohorts that were part of the original January 1992 shipment. In addition to the index cow, the cohort included one cow bearing the same unique brand which was located on the index farm before being destroyed and testing negative for BSE on July 11, 2006. In addition, two cows on the index farm were confirmed dead by the owner, one cow was confirmed slaughtered (USA, Nov. 1995), and 17 cows were sold by the index farm and are presumed dead based on the age of these animals and traditional beef cattle management practices.

The investigation revealed that the affected cow had two female calves (2004, 2005) during the two year period before the onset of clinical signs and was pregnant at the time of its death. It has been verified that neither calf was registered by birth date in the Canadian Cattle Identification Agency database, a requirement for export to some countries. The 2004 calf was sold in December 2005 and entered a feedlot in western Canada (Saskatchewan or Alberta); it either died in the feedlot or was slaughtered in a Canadian plant at a young age. It is known that a Canadian Cattle Identification Agency (CCIA) tag was assigned to this calf, but there is no retirement history for the tag in the CCIA’s database. The 2005 heifer calf is also presumed to be dead, as it was pastured with the index cow, but did not return from pasture at the end of the pasture season.

The carcass and hide from the BSE positive case, along with other contaminated materials, were placed under control and deep buried in an area that complied with provincial environmental regulations. No part of the cow’s carcass entered the human food or animal feed chain.

Feed Investigation

In view of the length of time the index cow lived on the premises, the CFIA conducted a review of feed and management practices on the index farm.

Interviews with the farm’s owners, a review of their records, and tours of the premises all support the farm as a dedicated cow-calf operation with no other commercial livestock species present. All available information indicates the cattle only had access to feed products appropriate for cattle.

Feeds consumed before 1997, at the index premises or any previous locations, may have contained meat and bone meal (MBM) which were permitted under the regulations of the time. Formulations and sources of MBM, if used, were not available, so it was impossible to determine whether there were any links to feeds identified in previous cases.

Investigation Overview

Canada has confirmed its sixth case of BSE. The five previous cases of BSE found in Canada were characterised as being similar to the majority of the BSE cases found around the world; however, this sixth case is a less prevalent strain of BSE which has also been reported in Europe and in the U.S.

With refinement and advancement in diagnostic test methods, scientists have only very recently demonstrated the existence of more than one strain of BSE, although multiple strains are known to occur in both human (CJD) and sheep (scrapie) prion diseases.

This less prevalent BSE strain is more difficult to detect and affects mainly older animals. Of the more than 200,000 BSE cases recorded worldwide, less than 100 are known to have been infected with different BSE strains. There is some speculation that the discovery of these different strains came to light as a result of the enhanced BSE surveillance programs occurring worldwide.

Relevant Considerations

The safety of meat 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 is the most effective single measure protecting consumers in Canada and importing countries from exposure to BSE infectivity in meat products.

On June 26, 2006, the CFIA announced that it is banning cattle tissues capable of transmitting BSE from all animal feeds, pet foods, and fertilizers. Such tissues have been prohibited from inclusion in feed produced for cattle, sheep, goats and other ruminant species since 1997. The enhancement will significantly accelerate Canada’s progress toward eradicating the disease from the national cattle herd by preventing more than 99% of any potential BSE infectivity from entering the Canadian feed system, and thereby eliminate the potential for cross contamination during production, transportation or storage.