Final TB-linked B.C. herd released

The last of 38 cattle herds subject to trace-out in connection with last November’s bovine tuberculosis case in British Columbia has been released from movement controls.

The Canadian Food Inspection Agency announced removal of the last restriction Sept. 23 and said trace-in efforts, designed to identify and eliminate the source of the disease if possible, are beginning this fall.

The investigation stemmed from discovery of one TB-infected animal traced to a ranch in B.C.’s southern interior on Nov. 9, 2018. Three more infected cattle in that herd were later confirmed with the illness and the entire herd was killed.

Trace-out activities, which involve testing herds that received animals from the infected herd within the previous seven years, eventually involved 15 herds in B.C., 22 in Alberta and one in Saskatchewan. No further cases of bovine TB were found.

Analysis of samples from the B.C. cases showed it was a different strain than the one that infected six cattle from southern Alberta in 2016, the CFIA said.

Trace-in activities involve herds with animals that were introduced to the infected herd over the past five years with the goal of finding the source.

“Although an exact determination of the source of infection is not always possible, the trace-in activities reduce the risk of undetected bovine TB within Canada’s livestock population,” the CFIA said in its explanation of trace-in.

“Trace-in activities also can help determine if bovine TB program adjustments are required in areas such as import controls, encouraging improved biosecurity measures and managing the potential risks associated with infected wildlife.”

Bovine tuberculosis is a federally reportable disease, which means the CFIA has a mandate to prevent its introduction and spread.

However, bovine TB can remain dormant in animals for years without causing symptoms and can take years to kill an infected animal. Those infected can also spread the disease to herdmates before showing any signs themselves.

That makes it difficult to find and control.

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