Bovine TB probe’s focus turns to infected herd

(Photo courtesy Canada Beef Inc.)

With no new cases of bovine tuberculosis discovered on the Prairies since mid-November, federal officials are now turning their focus to how the disease got into half a dozen cattle in the region last fall.

The Canadian Food Inspection Agency said Friday it has finished TB-screening and depopulating all mature cattle from 18 properties that have been deemed infected since September. In all, about 10,000 mature cattle and calves have been ordered destroyed, the agency said.

Any cattle from that group showing reactions to the initial screening test were checked post-mortem for bovine TB-related lesions, CFIA said — but the number of infected cattle remains at six, all from the same farming operation.

“While there was strong evidence that there could have been a high risk of disease spread, the initial test results are showing a more encouraging outcome,” the agency said in a statement.

Given the evidence so far, CFIA said its investigation will now focus on the single infected farming operation, though it noted “this path forward is only possible as long as no new cases of tuberculosis are identified.”

That means the agency’s trace-in and trace-out investigations associated with the one infected farming operation will continue, but tracing activities will not be conducted on the herds that commingled with the infected herds — as long as no TB-infected animals are identified from those other herds.

Following “accepted animal disease investigation practices,” and based on information obtained during the “initial phase” of its investigation, CFIA said it can now limit its tracing activities to the one farming operation, which means identifying the herds of origin for all animals introduced into the infected operation over the past five years.

The agency noted its decision stems also from seeking “a balance between the impact of the path forward on affected producers and our obligations to our international trading partners.”

The agency’s probe follows the discovery of one Alberta cow that tested positive for bovine TB when it was slaughtered at a U.S. packing plant in late September 2016.

CFIA said its evidence shows “low” risk that the disease was further transmitted by cattle that commingled with cattle from the infected farming operation while they were out on community pasture.

Furthermore, the agency said, “we have also eliminated the risk of further spread of tuberculosis since all mature cattle have been depopulated.”

Tracing activities will now focus on identifying the source of the infection, CFIA said, but added that testing of herds identified through these traces will begin in the fall, because calving season has already started in Western Canada.

Waiting until fall “will minimize stress on cows that are pregnant or have recently given birth” and “will also allow cattle from these low-risk herds to proceed to summer pasture.”

As for the 28,000-odd cattle on the 58 properties still under quarantine that received animals from the infected farming operation, CFIA said it’s still conducting screening on those animals. The properties include 51 in Alberta and seven in Saskatchewan, mainly in southeastern Alberta and southwestern Saskatchewan.

Only animals that react to the tests will be slaughtered and sent for “enhanced” post-mortems, CFIA said. Herds that have no reactors can be released from quarantine. The number of properties released from quarantine since the investigation began now sits at eight.

Compensation payments to Alberta producers whose herds under quarantine are being processed through the Canada-Alberta Bovine Tuberculosis Assistance Initiative (CABTAI), under the AgriRecovery program.

CABTAI covers “extraordinary costs” such as feeding and water infrastructure, feed for animals, transportation, cleaning and disinfection and “interest costs on loans due to the circumstances.”

Quarantined Saskatchewan producers can contact the provincial government directly for “similar support,” CFIA said.

Producers that were owners of the commingled herds will be able to go ahead with cleaning and disinfection under CFIA oversight — including a 45-day waiting period of warmer temperatures “to kill any bacteria remaining in the environment” — after which the producers will be allowed to restock.

To confirm the effectiveness of the clean-ups, CFIA said, restocked cattle will be tested six and 18 months after entry onto the premises.

Wildlife is considered “unlikely” to be the source of the TB bacterium in this outbreak, CFIA said previously.

The TB strain in this case has never been seen before in Canadian livestock, wildlife or people, but is “closely related” to a strain originating from cattle in central Mexico in 1997.

The agency grants that the source of an infection “can be difficult to identify, especially with cases that occur far from places where bovine TB is known to be present in wild animals.” — Network

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