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

BACKGROUND

On February 7, 2008 a private veterinarian in Northern Alberta euthanized and sampled a Holstein cow under Canada's National BSE Surveillance Program. Brain samples from this animal were sent to the Alberta Agriculture and Food (AAF) laboratory where they were screened for BSE using a Bio-Rad rapid test on February 13, 2008. The result of this preliminary test did not rule out BSE. In accordance with the prescribed testing protocol, the test was repeated and on February 14, 2008 produced a reaction a second time. Brain samples were then sent to the National BSE Reference Laboratory in Lethbridge, AB. Additional rapid tests for BSE (Prionics-Check PrioStrip and Prionics-Check Western) were conducted at the National BSE Reference Laboratory to validate the result of the screening test and were positive on February 19 and 20, 2008, respectively. The Hybrid Western Blot was positive on February 20, 2008 and on February 22, 2008, the Scrapie Associated Fibril Immunoblot was positive. On February 25, 2008, BSE was confirmed using the immunohistochemistry procedure. The carcass was secured at the sampling site, and was subsequently transferred to the CFIA Laboratory in Lethbridge 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 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 December 21, 2001 and it was 73 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 was approximately one month, during which the animal displayed progressive signs of impaired locomotion, culminating in the animal becoming non-ambulatory (downer). When examined by a private practitioner on February 7, 2008, the animal was recumbent. The practitioner and producer determined that the animal should be euthanized . 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. The feed cohort was determined to comprise 114 animals, which along with the case animal, were raised on the farm. Animals which were sold at less than one week of age for fattening and subsequent slaughter, without having access to any commercially prepared feeds, were excluded from the feed cohort investigation, because they were not exposed to the same potentially contaminated feed as the case animal. The trace-out investigation of the feed cohort located 13 live animals on the case farm. Three of the animals have since been humanely destroyed; their carcasses, and that of the case animal, disposed of by incineration. In recognition of the fact that BSE in not a contagious disease, ten animals are being retained, under quarantine, to allow for calving or collection of valuable genetic material. Subsequent to these events, the animals will be humanely destroyed and their carcasses incinerated in accordance with the OIE recommendations. The following is the disposition of the remaining 101 animals in the feed cohort:

• 41 animals were traced and confirmed to have died or been slaughtered,
• 56 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,
• One animal was determined to be untraceable.

The investigation revealed that the case animal had two calves born within the previous two years. The CFIA no longer requires the destruction of calves of BSE positive cows born within 24 months of the development of clinical signs, in accordance with the current Bovine Spongiform Encephalopathy Chapter of the OIE Terrestrial Animal Health Code (2007). However, the CFIA continues to trace calves born to a positive female in respect of the current export certification requirements of some importing countries. The 2006 and 2007 progeny were located on the case farm and were humanely destroyed to ensure Canada’s continued compliance with certain export certification requirements. Their carcasses were incinerated at the National BSE Reference Laboratory.

FEED INVESTIGATION

The feed investigation focused 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 cattle to be the only commercially farmed species present. Other animals present included a dog, several cats, and rabbits. Pet food is considered to contain prohibited material and investigators confirmed it was stored and fed separately from other feeds and animals.

There was no pasture use on the farm and all forages (hay and silages) were grown on land fertilized with commercial fertilizer and harvested using farm-owned equipment. Non-forage feed products included four different commercially prepared complete feeds, mineralized salt blocks, and loose mineral feeds supplied by two commercial feed manufacturers and one retail outlet.

Two of the complete feeds (the dairy ration and the heifer ration) were delivered in bulk and transferred directly into their respective bulk storage bins. A third feed, the dry cow ration, was delivered in 25 kg bags and fed directly to dry cows and pregnant heifers only. A complete starter ration for calves was also purchased in bags.

Consistent with management practices for all heifer calves on the farm, the case animal was housed in a single enclosed hutch for approximately the first eight weeks of life, and then moved through a series of group pens with other heifers of similar age and size. Calves were initially fed colostrum, followed by milk and calf starter beginning at three days of age and continuing to approximately eight weeks of age. Heifer calves were introduced to the commercial heifer and dairy rations beginning at approximately eight weeks of age and pail-fed increasing amounts (in mixed proportion) until approximately eight months of age. From approximately eight to 13 months of age, heifers were fed heifer ration with mineral feeds. Forages were provided throughout. Feed mixing and handling practices described for the farm preclude feeding of the dry cow ration to heifers less than 12 months of age. Therefore, feeds to which the case animal may have been exposed and which warranted investigation were: calf starter, heifer ration, dairy ration, mineralized salt blocks, and mineral feeds.

Investigation at the commercial manufacturer supplying the loose mineral products identified that production of these was in a facility handling prohibited material but with dedicated equipment and in accordance with procedures which ruled them out as a possible source of contamination. Similarly, the mineralized salt blocks were manufactured in a specialized facility which did not handle prohibited material.

Calf starter was supplied exclusively by one commercial manufacturer whereas supply of the heifer and dairy rations alternated between this facility and a second manufacturer. Both facilities cross utilized equipment in the manufacture and delivery of feeds for ruminants and those containing prohibited material. Prohibited material was supplied to both facilities from the same rendering facility which also supplied prohibited material to feed suppliers identified in previous BSE cases.

The facility supplying approximately half of the heifer and dairy rations had documented procedures in place to prevent contamination of ruminant feeds with prohibited material. The facility providing the remainder of the heifer and dairy rations and all the calf starter reported procedures were in place to prevent contamination but most production records did not include documentation that these procedures were followed.

Four deliveries of calf starter were identified during the time frame of interest and subsequently investigated. There was no means of tracing the deliveries to specific production lots so all lots manufactured during the time frame of interest (total of six) were investigated. Production records identified one of the lots followed a feed containing prohibited material without proper cleanout of the production equipment (pellet mill).

Seven deliveries of heifer ration were identified during the time frame of interest and investigated. None of the records examined indicated contamination with prohibited material occurred during their manufacture, transport or storage.

Twenty-eight deliveries of dairy ration were identified during the time frame of interest and investigated. Production records identified one of these feeds was manufactured after a feed containing prohibited material and without proper cleanout of the production equipment (pellet mill). This feed was delivered to the farm when the case animal was 38 days of age and precedes the estimated age (56 days) at which dairy ration was first offered. A later delivery of dairy ration when the case animal was slightly less than eight months of age may have also had carryover amounts of a feed containing prohibited material due to improper sequencing of a pre-pellet holding bin.

Feeding a contaminated calf starter within the first two months of life is one possible source of exposure to infectious material for the case animal. Additionally, evidence suggests that two other rations supplied to the farm during the time frame of interest may have been cross-contaminated with feeds containing prohibited material and potentially fed to the case animal. In the absence of complete documentation additional exposures can not 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, and the BSE surveillance results to date, including this new case, reflect an extremely low level of BSE in Canada. In essence, the case confirms what was already known about an extremely low level of BSE infectivity having existed in Canada’s feed system during the late 1990s and early 2000s within a previously determined geographic area and time interval.

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 as supported by the feed investigation findings. The investigation into the current case identified a few possibilities but it was impossible to determine the exact source of exposure.

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 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 12 positive animals detected among the over 212 000 targeted tests conducted since 2003. Such detections demonstrate the effectiveness and integrity of Canada's surveillance system. Canada’s controlled BSE risk status under the OIE’s science-based system also 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 BSE in Canada.

OTHER RELEVANT INFORMATION

With respect to BSE, 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 material (SRM)-those 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. The detection of BSE in a few animals born after the 1997 feed ban is not unexpected and does not indicate a failure of the measures in place to reduce and eventually eradicate BSE.

Canada’s own BSE experience has served to emphasize the importance of addressing opportunities for cross-contamination of ruminant rations and cross-feeding of ruminants with rations containing prohibited proteins. Although the 1997 feed ban regulations include provisions addressing these risks, the detection of BSE cases in cattle born after 1997 contributed to Canada’s decision to implement additional regulations enhancing Canada’s feed ban on July 12, 2007. Principally, the enhancements require the removal and redirection of SRM from all animal feed, pet food and fertilizers.

The enhanced feed ban limits potential opportunities for BSE infectivity to contaminate feeds for ruminants by controlling all activities related to the movement of SRM, its distribution, processing, destruction, disposal or alternative uses through a system of permits. This ensures that these materials do not enter the human and animal food chains or the fertilizer system and effectively contains any potential BSE infectivity thereby preventing exposure of susceptible species to the BSE agent.

This enhancement will significantly 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.