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

Background

On April 8, 2006 a Holstein cow on a dairy farm in the Fraser Valley area of British Columbia was euthanized and sampled under Canada's National BSE Surveillance Program. The carcass was placed under detention and held pending testing results. Brain samples from this animal were sent to a British Columbia provincial laboratory where they were screened for BSE using a Prionics rapid test. The sample produced an inconclusive reaction on April 11, 2006. In accordance with the prescribed testing protocol, the test was repeated on April 12 and 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 by the immunohistochemistry procedure on April 16, 2006. The carcass was secured from the sampling site and, after additional tissues were taken for research purposes, transferred to the Canadian Food Inspection Agency (CFIA) Lethbridge laboratory and subsequently incinerated. No part of the carcass entered the human food supply or animal feed chain.

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

• calves born to the affected cow during the two years prior to the onset of clinical signs;
• the birth cohort (all cattle born in the same herd as, and within 12 months of the birth of, the  BSE affected animal) or the feed cohort (all cattle which, during their first year of life, were reared with the BSE affected animal during its first year of life, and which investigation showed consumed the same potentially contaminated feed during the period); and
• feed to which the animal may have been exposed early in its life.

Animal Investigation

The affected Holstein cow was born on April 29, 2000, and was 71 months, or circa six years old at the time of death. It had been moved from its farm of birth, to the index premises, just over one year prior to the onset of clinical signs of disease. 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). At that time a decision was made to euthanize the animal and, because it met the inclusion criteria of Canada's National BSE Surveillance Program, arrangements were made to forward appropriate samples for laboratory evaluation.

The investigation revealed that the affected cow had two male calves born during the two years prior to the onset of clinical signs (born March 27, 2005 and April 7, 2004). CFIA investigators determined that the 2005 calf was either euthanized shortly after birth or entered the fattening/slaughter stream at a young age and subsequently died or was slaughtered. The 2004 calf was determined to have entered the fattening / slaughter stream and subsequently died or was slaughtered.

The birth farm was also a dairy operation. The feed cohort was determined to comprise 146 animals which, along with the affected animal, were raised on the birth farm. This cohort included Holstein females and males raised as breeding stock. 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 index case. The trace-out investigation of the cohort located 23 live animals on the index premise and in other herds to which they had been sold. Twenty-two of these animals have been euthanized, sampled and tested negative for BSE. Disposal of the carcasses was by incineration. The remaining animal (under CFIA quarantine) is very near to calving, and for this reason its destruction and testing has been postponed. Because the cohort cattle would now be five to seven years of age, many had previously been slaughtered or died of causes unrelated to BSE. The following is the disposition of the remaining 123 animals in the cohort:

• 67 animals were traced and confirmed to have died or been slaughtered (one animal had previously been tested under Canada's National BSE Surveillance Program with negative results);
• 8 animals were traced and presumed to have died or been slaughtered at other locations
• 15 were exported to the USA for breeding purposes (this information has been forwarded to US authorities for follow up)
• 33 animals were determined to be untraceable because of inadequate records

Feed Investigation

A thorough and detailed feed investigation was conducted at the birth farm to identify all of the feed materials used, the suppliers and sources of these products, and the feeding and feed storage management practices. Investigators focussed on all potential avenues of direct exposure to prohibited material, as well as potential areas of cross-contamination. Compliance with regulatory requirements of the feed ban was assessed throughout the investigation.

Investigation at the birth farm revealed it to be a dedicated dairy operation with no other livestock species present. All feed products to which the index animal had access were intended for feeding to ruminants and consisted of farm-grown or purchased forages (hay and silage) as well as commercially prepared feed. Pets on the farm (cats and one dog) were fed pet food that was stored and fed away from the dairy operation, thus eliminating these rations as a potential source of prohibited material to the BSE positive animal. Consistent with this farm's practices, the index animal was housed in a series of indoor pens and did not have access to fertilizers, compost or other potential sources of prohibited material.

A review of feed storage and feeding practices identified the use of bagged, block and bulk commercially-prepared products. The only on-farm mixing equipment was a mixer wagon used to combine forages and commercially prepared lactation rations for the milking herd which was never shared or loaned off-farm.

All commercially prepared rations were purchased from a single supplier. Five products (representing the largest quantities the animal consumed) were manufactured by the supplier, in its own facility. A further six products (specialty products such as milk replacer and mineral/salt blocks) were manufactured in facilities owned by other companies.

Three of four facilities supplying specialty products (milk replacer, salt and mineral blocks) were dedicated free of all ingredients prohibited from use in ruminant feeds. The fourth facility (a supplier of mineral blocks to the birth farm) did handle prohibited material. Examination of the mixing records at this facility, for products to which the index animal may have been exposed, revealed improper sequencing between the manufacture of one lot of mineral blocks and a previous product that contained prohibited material. However, the nature of the product and the age of potential exposure (beginning at 6 months) make this an unlikely source of exposure of the affected animal as consumption would be extremely low.

The five major products manufactured in-house by the primary supplier, representing the largest quantities of feed the animal accessed (calf starter, calf grower, 2 different lactation rations and a dry cow ration), were formulated in a facility dedicated free of ingredients prohibited from use in ruminant feeds. The investigation confirmed the integrity of the procedures and equipment dedicated to all aspects of ingredient storage, processing, mixing, pelleting and feed storage, ruling out the possibility of cross-contamination occurring within the facility. However, the investigation also revealed that the facility shared an ingredient receiving system and bulk feed delivery trucks with another facility that did use prohibited materials in the manufacture of feeds for non-ruminant species. Under these circumstances, cross-contamination of feeds manufactured by the primary supplier could have occurred as a result of either the shared ingredient receiving system or during the delivery of bulk feed.

Interviews with staff at the latter facility identified that flushing procedures were used to prevent cross-contamination of ingredients and feeds at these points. However, written procedures in place at the time did not identify these requirements, and it was also not the practice at the time of production to document when flushing procedures were applied.

The risk of exposure of the index animal to a potentially contaminated feed cannot be ascribed to any specific product. In the absence of written records of procedures used to prevent cross-contamination, and lack of documentation to demonstrate these procedures were followed, it is not possible to verify actual production practices in place or to assess occurrence of possible failures. The effect of this is to identify all bagged feeds manufactured by this facility as representing a similar risk (due to shared ingredient receiving) and all bulk feeds as posing a similar risk (due to shared ingredient receiving and shared bulk delivery).

Identification of suppliers to the facility with shared ingredient receiving and bulk delivery trucks revealed five different sources of prohibited material. One of the major suppliers of prohibited material to this facility was the sole supplier to the facility servicing the birth farm of the BSE-affected cow diagnosed on January 23, 2006. These two most recent cases share the same susceptibility period as a result of their similar birth dates.

The findings of this investigation indicate that compliance with the1997 feed ban regulations was largely achieved through adoption of dedicated manufacturing facilities. Despite this, it is evident that opportunities for cross-contamination remained where conveyances and equipment were cross-utilized.

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 suggest that the major rations could have become contaminated during manufacture or distribution.

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 occurrence of this fifth case of BSE in Canada is consistent with the geographical and temporal clusters proposed therein.

The location of the index case's birth farm may suggest yet an additional geographic cluster. However, given its possible relationship with a previously identified source of prohibited material, this occurrence similarly suggests that the feed distribution area associated with the existing geographic cluster may not be confined to Alberta, but may include additional Western provinces. The timing of the presumed exposure of Cases 4 and 5, born in the same year and month, suggests an insult to the feed system separate and apart from the one associated with the previous cases born in 1996 - 1997. Cases 4 and 5 suggest that the previously acknowledged and undetected first generation indigenous BSE cluster contained a minimum of two animals.

The detection of BSE affected animals born after the introduction of a feed ban is not unique to Canada, and does not signal failure of the measures in place to reduce and eventually eradicate BSE. Measures equivalent to Canada's feed ban have been demonstrated to curtail the amplification and spread of BSE in cattle and be likely to eliminate the disease over time. Additional measures are currently being considered to further reduce the potential for contamination of ruminant feed, and 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.

CFIA significantly increased the frequency of inspection of the animal feed system beginning in 2000. Since that time there has been an increasing level of compliance with the requirements of the feed ban.

Since the detection of BSE in Canada in May 2003, the increased testing of animals from the high risk categories (including this downer animal) was directed at determining the level of BSE in Canada, while monitoring the effectiveness of the suite of mitigating measures in place. It is reassuring that, among over 105,000 targeted tests conducted since 2003, this is only the fifth positive animal detected, indicating an extremely low level of BSE in Canada. Such detections demonstrate the integrity of Canada's surveillance system, the level of awareness which exists at all levels of the animal and food production system and the commitment of Canadian producers and veterinarians to the elimination of this disease.