Bovine tuberculosis in British Columbia (2018) - case response overview

Introduction

In November 2018, the Canadian Food Inspection Agency (CFIA) responded to a case of bovine tuberculosis (TB) detected in a cow from a cow-calf operation in British Columbia. Once the investigation was completed, only one herd was found to be positive with 4 animals showing lesions and confirmed laboratory culture results for Mycobacterium bovis. Given the outcome of the case response, British Columbia continues to be recognized as being free from bovine TB. The bovine TB free status of all other provinces also remains in place.

The strength of Canada's bovine TB program supported uninterrupted international market access for Canadian cattle and meat products during the course of the response and this mitigated any impacts on the overall Canadian cattle sector.

The cooperation of individual producers involved in the response and the engagement with their industry associations were vital to the effectiveness of the CFIA's response.

Detection

The CFIA routinely collects tissue samples at slaughter facilities for testing under the Granuloma Submission Program to support bovine TB surveillance in Canada. On November 9, the CFIA's Fallowfield laboratory reported Polymerase Chain Reaction (PCR) positive results for a sample collected from an animal slaughtered on October 26 at a federally registered establishment in Alberta.

Based on the PCR results, the CFIA began its disease response. Laboratory culture testing and diagnostic whole genome sequencing was completed while the disease response was underway. The diagnostic testing determined that the M. bovis strain isolated from the positive animals is most genetically related to strains isolated in the United States of America (USA) from fed cattle of Mexican or unknown origin, and is not linked to previous cases in wildlife, humans or livestock in Canada.

Index animal history

The origin of the animal was traced to a beef cow-calf operation in the southern interior of British Columbia. The cow (age unknown) had been culled on October 24, 2018, shipped to a stockyard yard in Alberta on October 25, 2018 and slaughtered on October 26, 2018 at a federally registered establishment in southern Alberta.

Overview of the disease investigation and eradication measures

Disease eradication and investigation measures were initiated on the index premises. Eradication measures included movement controls followed by herd testing of all animals over six months of age.

Following herd testing, all bovine animals were destroyed with post-mortem examinations. Animals with a reaction or non-negative result to a screening test were subject to an enhanced post-mortem inspection and sample collection for histopathology and culture. Animals without a reaction or positive result to a screening test were subject to routine post mortem inspection . Any detection of granulomas or gross visible lesions required sample collection and submission for histopathology and culture. Three additional animals in the index herd were determined to be positive for bovine TB. There has been no evidence of the spread of infection to any animals including wildlife outside of the index herd.

The index premises was required to undergo cleaning and disinfection procedures prior to restocking. One pasture was not permitted for restocking as the producers elected to allow the pasture to remain fallow for a two-year period, which will be completed in 2021.

The disease investigation activities related to the index farm included: an epidemiologic investigation of herd history, inquiry of risk factors with respect to the source of infection and tracing of all herds epidemiologically linked to the index herd.

Epidemiologically linked herds for further investigation were classified into one of the following groups based upon the type of exposure to the index animal and herd

• Contact herds
• Trace-out herds
• Trace-in herds
• Herds requiring repeat tests

Contact herds

Contact herds types are classified as high, moderate or low-risk herds based on the level of contact with the index herd. The investigation identified two major exposure contact types: low-risk direct contact due to fence line contact with the index herd (DCL) and high-risk direct contact via comingling with the index herd (DCH). Movement restrictions were placed on all direct contact exposed herds and herd testing was completed. Animals over 12 months in the low/moderate risk herds and animals over six months in the high risk herd were tested.

Nine direct contact herds were investigated. Herd testing was completed on the direct contact herds. Any reactors or screening test non-negative animals in the high and moderate risk herds were ordered destroyed with enhanced post mortem inspection and tissue sampling of any granulomatous lesions. Ancillary tests were completed for reactors in low risk herds and non-negatives were ordered destroyed with enhanced post mortem inspection.

All animals that were ordered destroyed were negative for bovine TB and movement restrictions removed from their herds.

Trace out herds

A trace out investigation was carried out to detect and prevent the spread of M. bovis infection from the infected herd/premises through the removal of an infected or exposed animal during the five years prior to when the infection was detected in the index animal. This investigation identified 2,612 animals. The majority of these animals were found to have been marketed to terminal feedlots and subsequently slaughtered or moved directly to slaughter and did not require further investigation.

Animals identified as still resident in feedlots at the time of the investigation were ordered destroyed and underwent enhanced or routine post mortem examination. Breeding herds with trace out animals present or which had previously come into direct contact with a trace out animal were placed under movement restrictions and subjected to herd testing. All trace out animals and any animals with a reaction or non-negative result to a screening test were ordered destroyed and underwent an enhanced post-mortem examination and sample collection for histopathology and culture.

All animals that were ordered destroyed were negative for bovine TB and movement restrictions removed from their herds.

Trace in herds

The trace-in investigation traced all animals introduced to the index farm in the eight years prior to the identification of the first bovine TB positive animals. Twelve herds in Western Canada were identified for testing in the trace in investigation. Trace-in herds required a herd test of all test eligible animals (12 months of age or older) and any reactors underwent ancillary testing. Animals with non-negative ancillary test results were ordered destroyed, underwent enhanced post mortem examination and sample collection for histopathological examination and culture.

All animals that were ordered destroyed were negative for bovine TB and movement restrictions removed from their herds.

Herds requiring repeat tests

Three herds (one direct contact herd and two trace-out herds) were tested a second time because of high levels of contact with the index herd or unidentifiable / untraceable animals. The second tests were completed between six and twelve months after the first testing.
Repeat herd testing provided added assurance that there were no latently M. bovis infected animals remaining in these herds.

Wildlife surveillance

The Province of British Columbia is conducting ongoing surveillance of wildlife in the vicinity of the index herd for evidence of bovine TB. To date there has been no evidence of bovine TB in wildlife in the vicinity of the index herd.

Cleaning and disinfection

The index premises was required to undergo cleaning and disinfection procedures prior to restocking. One pasture was not permitted for restocking as the producers elected to allow the pasture to remain fallow for a two-year period, which will be completed in 2021.

Source of infection

After testing over 23,000 animals in 42 herds in Western Canada and beginning wildlife surveillance activities in the vicinity of the index herd, the investigation has not identified any definitive source of infection for the index herd. Likewise there has been no evidence of the spread of infection to any animals including wildlife outside of the index herd. The CFIA is evaluating possible entry pathways of bovine TB from outside the country to determine if further preventive measures can prevent potential future incursions.

As a result of the 2016 and 2018 cases of bovine TB, the CFIA evaluated possible entry pathways of non-domestic strains of M. bovis into Canada. As a result of that evaluation, the CFIA worked with the United States Department of Agriculture to apply, effective May 1 2020, more stringent import controls (testing) on U.S. origin rodeo cattle prior to their importation into Canada.

Compensation

Compensation for nearly 1050 animals ordered destroyed, costs for transportation, disposal and destruction of the animals totalled $3.78 million. Approximately $3.2 million of the total compensation costs were paid directly to producers.

In addition, the Canada-British Columbia Bovine Tuberculosis Assistance Initiative (CBCBTAI), developed through AgriRecovery Framework, provided up to $1 million to producers who faced extraordinary costs as a result of their herd being quarantined or ordered destroyed. The program covered a portion of eligible costs related to feeding, veterinary expenses, extraordinary handling and cleaning & disinfection on sites where bovine tuberculosis was confirmed.

Lessons learned

Based on discussions with external stakeholders during and after the investigation, the CFIA noted a number of opportunities for improvements or updates in policy, operations and communications. Several measures were implemented in the course of the investigation.

• As with other animal disease responses in British Columbia, having a joint command with the BC Ministry of Agriculture was valuable. The benefits of this structure included: shared resources and expertise; consistent messaging and timing; and facilitating communications with respect to range management; and engagement with Indigenous stakeholders.
• There continue to be information management and technology challenges for disease responses. However, data management was improved through the use of new RFID ear tag readers and centralized data that was accessed through several reporting tools. This approach reduced the need for manual data entry and the related costs and potential for errors.
• There is industry interest in further discussions in regard to producer compensation, including costs that are not covered by Health of Animals Act and potential alternatives to herd destruction for herds with unique genetics. It will be beneficial to have the revised bovine TB hazard specific plan finalized prior to the next response to ensure clear direction for incident commanders and field staff. Also, more veterinary epidemiology capacity in the CFIA's Western Area would be beneficial for any future reportable disease response.
• The importance of effective communications with producers was highlighted by producers and their industry associations. The CFIA acknowledges the vital role that the province and industry associations played in communicating with producers. In particular, having ongoing representation from the BC Cattlemen's Association was extremely valuable.