In recent months, several cattle from herds in Alberta and Saskatchewan have tested positive for exposure to tuberculosis. The index animal — a beef cow — was identified at slaughter at a U.S. processing plant.
Since then several more suspects have been identified by skin testing. Over 22,000 cattle are affected by quarantines. A common feature of all these herds is that they were commingled in huge community pastures every summer.
There has been much public speculation regarding the source of the disease, with many of the cattle ranchers stating publicly and with considerable confidence that the wild elk herd in the nearby Suffield grasslands is the problem.
To date, there is no evidence to support those statements. Too frequently cervids, both wild and farmed, are used as a handy scapegoat for outbreaks even when evidence is to the contrary.
In fact, the trail points far south in the case of the most recent outbreak. The strain of TB involved has been identified as one first identified in cattle in central Mexico, then subsequently in Nebraska. It has never been identified in Canada until now.
It is interesting to recall the history of TB in cervids in Canada. A strain identified as being associated only with Riding Mountain Park was identified in wildlife in the park in the 1960s, but the focus at the time was eradication in domestic herds first. In that process, a cattle herd was identified as positive on the edge of the park, and testing of harvested elk showed positives in the wild as well. A decades-long eradication campaign has reduced incidence to less than one per cent in the wild and no cattle herds have been infected for a decade.
The next outbreak was in Alberta in the late 1980s, with the strain and source identified as elk imported from the U.S. — probably the Yellowstone region where TB still persists. Enforced destruction of all affected herds terminated that outbreak. The next incident in 1999 was in elk in an assembled herd in southern Ontario. The strain pointed to zoo stock in Eastern Canada as the source, and once again the destruction campaign appears to have been successful.
The most interesting was the next one in 2006 in southern Ontario once again. The single positive was a 17-year-old red deer female which was initially imported from New Zealand. Strain testing showed this to indeed be a New Zealand type of TB. Note that all the cases involve one feature: commingling.
Those are all the positives known in cervids in Canada, and the last TB positive in farmed cervids in Canada was over a decade ago. Exceptional disease-control measures were introduced in 1989 for all farmed cervids in Canada in response to that late-1980s TB outbreak in Alberta.
Initially, whole-herd testing using skin tests on the neck was required every year, then that was slowly relaxed to every three years and currently every five years. Cervid movement permits (CMPs) issued by CFIA district offices have been required since that same year before any movement is permitted of any cervid in Canada, both farmed and wild. Criteria for CMP issuance are negative status for both TB and brucellosis, except direct to slaughter. Testing and movement controls may have contributed to freedom from both diseases, and have demonstrated benefits for surveillance, traceability and export certification while imposing significant costs on producers and CFIA, and risks of injury or death for many animals.
The Canadian Cervid Alliance (CCA) has been pressing CFIA to begin the process of assessing the ongoing need for these burdensome tests. Given the history and status of both diseases, and the current nature of the industry, CCA felt that the pressure on producers, farmers and CFIA could be justifiably and safely reduced.
CFIA began that process of evaluation and risk assessment several years ago, and has concluded that the farmed elk herd in Canada is now in position to be declared free of TB and brucellosis. To maintain that status, only enhanced slaughter surveillance and targeted surveillance in specific areas will be necessary.
This is a great accomplishment — one that has been achieved with a huge amount of work and investment by both CFIA and producers, working co-operatively together.