Bovine Tuberculosis in Western Canada (2016) - Case Response Overview

Introduction

In September 2016, the Canadian Food Inspection Agency (CFIA) responded to a case of bovine tuberculosis (TB) detected in a cow from a cow-calf operation in Alberta. Once the investigation was completed, only one farm was found to be positive with 6 cows showing lesions and confirmed laboratory culture results for Mycobacterium bovis. Given the outcome of the case response, Alberta 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

On September 16, 2016, United States Department of Agriculture – Animal and Plant Health Inspection Service (USDA-APHIS) notified the Canadian Food Inspection Agency (CFIA) that a Canadian cow exported to the USA and slaughtered on September 6, 2016 was found to be a bovine TB suspect following post-mortem examination. Extensive lesions were found in the head and thorax of a mature beef cow. Subsequent testing by the USDA National Veterinary Services Laboratories (NVSL) in Ames, Iowa confirmed Polymerase Chain Reaction (PCR) positive results for Mycobacterium tuberculosis complex (MTC) and mycobacterial culture isolation of Mycobacterium bovis. Further diagnostic whole genome sequencing was performed by the USDA and found to be derived from a strain first identified in Mexico in 1997.

Index Animal History

The origin of the animal was traced to a beef cow-calf operation in the Jenner, Alberta area. The five year old animal had been culled on September 1, 2016, marketed through a local auction market, shipped to an assembly yard in Saskatchewan on September 2, 2016 and exported to the USA on September 5, 2016 for immediate slaughter in Long Prairie, Minnesota.

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 twelve months of age.

Following herd testing, all bovine animals were destroyed with post-mortem examination of all animals over twelve months of age. 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 reaction or positive result to a screening test were subject to standard post mortem inspection. Any detection of granulomas or gross visible lesions required sample collection and submission for histopathology and culture. Five 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.

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 for the past five years.

The disease investigation involved four categories of herd investigation based upon the type of exposure to the index animal/herd:

• Direct Contact Herds
• Trace-out Herds
• Trace-in Herds
• Buffer Zone Herds

Direct 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 on all animals over 12 months of age was completed.

Fifteen DCH herds were identified. Further investigation of those herds found exposure due to the commingling of twelve herds on summer grazing pasture, two herds on winter grazing pasture and one herd by shared bull use. This exposure was of sufficient duration and intensity for these herds to be considered as the same epidemiologic unit as the index herd until further diagnostic results determined the prevalence of M. bovis within each herd. Therefore, a risk-based decision was made to consider these 15 exposed herds as Presumed Infected. Disease eradication measures, namely movement controls, whole-herd depopulation of all exposed bovine animals, cleaning and disinfection of contaminated areas on the premises, and monitoring of re-stocked livestock, were applied.

All 15 herds completed herd testing, depopulation, post mortem inspection and histopathology of enhanced post mortem tissue samples. No evidence of bovine TB was identified. Therefore, the full suite of disease investigation procedures including tracing all animal movements out (trace-out), all animal movements in (trace-in) over the 5 year critical period, contact herd investigations, buffer zone testing and wildlife surveillance were not required on these premises.

There were 13 low-risk contact herds due to fence line contact during summer grazing with the index herd. Herd testing was completed on the DCL herds. Any reactors or screening test non-negative animals were ordered destroyed with standard post mortem inspection and tissue sampling of any granulomatous lesions.

If the animals ordered destroyed were negative for bovine TB, no further action was required and the herd was released from quarantine.

Trace Out Herds

A trace out investigation was carried out in order 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 over 2,700 animals as trace outs. 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 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.

If the animals ordered destroyed were negative for bovine TB, no further action was required and the herd was released from quarantine.

Trace In Herds

The trace-in investigation traced all animals introduced to the index farm in the 5 years prior to the identification of the first bovine TB positive animals. Sixty-eight 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.

If the animals ordered destroyed were negative for bovine TB, no further action was required and the herd was released from quarantine.

Buffer Zone Herds and Wildlife Surveillance

Resident cattle herds within a five kilometer radius of the index premises that were not covered by other testing activities were subjected to herd testing with the same protocol as the trace in herds.

This testing is intended to detect any spread of the disease within domestic cattle in the local area. It also helps to determine if wildlife were a potential a potential source of infection.

With collaboration from the Province of Alberta, surveillance of wildlife in the vicinity of the index herd for evidence of bovine TB is ongoing. To date there has been no evidence of bovine TB in wildlife in the vicinity of the index herd.

Cleaning and Disinfection

All premises including community pastures which were classified as infected or presumed infected were required to undergo cleaning and disinfection. As of the writing of this report all premises with the exception of one have completed the necessary requirements.

Compensation

Compensation for nearly 12,000 animals ordered destroyed, costs for transportation, disposal and destruction of the animals totalled $42.8 million. Approximately $39 million of the total compensation costs were paid directly to producers.

In addition, the Canada-Alberta Bovine Tuberculosis Assistance Initiative (CABTAI), developed through AgriRecovery Framework, provided up to $16.7 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 feed and yardage, interest carrying costs, transportation and infrastructure.

Source of Infection

After testing over 34,000 animals on over 145 farms in Western Canada 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.

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.

• Updates to the bovine TB policy and procedures are being implemented to ensure that the challenges of a complex investigation involving large herds and community pastures are reflected in the CFIA's disease response framework.
• The need to continue to work with the cattle industry for further improvements to traceability in Canada was acknowledged.
• It was recognized that emergency response capacity, based on well trained and available employees, is critical to successful outcomes in future disease investigations. The CFIA is implementing an internal reorganization that will consolidate emergency management responsibilities within the Operations Branch to optimize resources for effective responses in the future.
• The complex testing environment for bovine TB e.g. histology and bacterial cultures requiring up to 14 weeks in a Level 3 biocontainment laboratory) contributed to challenges in the delivery of laboratory support. Over the course of the response, adjustments were made to internal communications between the field and laboratory which resulted in improved delivery.

• The importance of effective communications with producers was highlighted by producers and their industry associations who also noted that communications improved throughout the investigation.

  The CFIA also acknowledges the vital role that industry associations played in communicating with producers. In particular, having ongoing representation from the Alberta Beef producers in the CFIA Area Emergency Operations Centre was extremely valuable.