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Bovine tuberculosis surveillance gets a facelift

A case of bovine TB in Manitoba’s domestic herd hasn't been seen since 2008

The Canadian Food Inspection Agency (CFIA) is wrapping up an ambitious round of bovine tuberculosis testing of cattle, wild elk and deer in and around Riding Mountain National Park in west-central Manitoba as the first step in easing TB surveillance measures for producers living in this area.

It can’t come soon enough for the producers in the Riding Mountain Eradication Area (REMA).

It’s going on 12 years that beef producers in the RMEA have been required to present their herds to CFIA for routine on-farm testing as often as every second year in some locations.

There hasn’t been a case of bovine TB in Manitoba’s domestic herd since 2008, yet the RMEA surveillance program remains unchanged because wild elk in the park are a known reservoir for the disease.

It’s taken a toll on producers, says bovine TB co-ordinator Allan Preston. Not only on those who’ve already called it quits, but those still committed to making a go of it despite the stress and ever-present dread of having TB turn up again.

Surveillance currently takes up half of the standing TB management plan’s annual $2-million budget and many feel it would be better for all concerned if more of that money could be spent on research, risk mitigation and disease prevention.

Preston, a beef producer himself and former practising veterinarian and assistant deputy minister of agriculture in Manitoba was appointed to his position by the provincial and federal governments in December 2012 at the urging of Manitoba Beef Producers (MBP). His role has since been extended to the end of this year.

This was part of the MBP’s continuing campaign in support of producers in the RMEA who have had to bear the burden of the heightened security measures on behalf of all Manitoba producers. Their co-operation with the program allowed Manitoba, including the RMEA, to regain its TB-free status in 2006 and maintain it since then.

The CFIA created the RMEA on January 1, 2003, on the heels of the TB outbreak of the early 2000s, after the USDA decision to downgrade Manitoba’s TB status in the summer of 2002. To this day, the U.S. requires negative individual tests on all cattle and bison of breeding potential from anywhere in Manitoba before they’re allowed in.

As of this summer there were 429 herds (41,052 head) in the RMEA with 37 herds (3,367 head) in the core area.

Special testing program

A big part of Preston’s initial work involved bringing together the various stakeholders — MBP, two federal departments, two federal agencies, two provincial departments, the Manitoba Wildlife Federation and a large First Nations community — to decide on a path forward.

Using wildlife modelling it was determined that 102 elk and 135 white-tailed deer would need to test negative to prove TB had reached an undetectable level. The CFIA also chose to test 5,000 cattle from 55 herds in the RMEA.

At an undetectable level, Preston says he would feel comfortable saying TB has been pushed back far enough that it would no longer be a problem. To eradicate it they would have to eliminate all wild elk and deer from the park and that was never in the cards.

Testing the wild population ran into a couple of hitches earlier on. Hunters were required to submit samples but only six elk and 95 deer had been submitted up to February of this year and by then it was discovered that the elk and deer populations in the park were lower than expected.

Preston says Parks Canada then stepped up with a program to capture, kill, inspect and test 46 elk and 40 deer, and donate the meat from healthy animals.

The remaining elk samples were collected by the conventional method of capturing animals for a blood sample, then fitting them with an ID collar and releasing them. Positive ones would be recaptured and euthanized to confirm a diagnosis with a culture test that can take up to four months.

All elk removed from the park were cultured as well as five of the captured animals.

Results and implications

On May 12 one elk cow cultured positive. Fortunately she was born in the spring of 2003, making her a remnant of the early 2000 outbreak. “Picking up one of those old cows or bulls wasn’t unexpected,” Preston says. “Where a positive in the elk population would be of greater concern is finding one born after 2004 because that’s the area that would tell us if we have the disease still percolating in the wild.”

To date, there has not been a positive wild elk born after 2004.

All of the deer samples came back clean. Finding a positive deer would have been uneventful at any rate because TB in this population was a spillover from the previous high level in wild elk. The first of 11 deer cases was confirmed in 2001 and the last in 2009.

Finding the one old positive elk cow will have implications for ongoing surveillance of the elk population because it means that TB in the wild isn’t yet at an undetectable level. However, Preston says it shouldn’t affect plans to reduce the testing of the domestic cattle herd because the elk was taken from deep in the core area of the park, where the risk to cattle would have been minimal.

Testing of the RMEA domestic herd is focused mainly on the rural municipalities of Rossburn to the south of the park and Grandview to the north where past outbreaks have occurred. Fourteen herds have been depopulated since the start of Manitoba’s bovine TB management plan in 1990.

As of late August, 51 herds had been tested covering 3,600 head and two remained to be done. Six head reacted to the caudal tail fold test. This is in line with the expected reactor rate. Those animals were retested using a two-stage blood test. Five of the animals have been cleared and the results were still pending on the last one.

“Finding one or more positives in the domestic herd wouldn’t be the end of the world,” Preston says. “The CFIA has a well-exercised drill for dealing with that and the clock starts ticking. We have 48 months from the first herd and if we have a second herd in that 48-month window, then our TB status is at risk.”

The goal of the working group is to reduce the amount of live testing at the farm and rely on packing plant data for cattle from the RMEA to provide the necessary surveillance.

“The reduced testing will be much more targeted and strategic based on qualitative and quantitative risk assessments of the RMEA producers,” Preston explains.

TB surveillance at packing plants is a long-standing program in Canada and the U.S. In Canada, CFIA personnel on the floor at federally inspected plants and veterinarians supervising other abattoirs check for TB when they carry out regular health inspections. Unfortunately, a test run on this concept last winter had disappointing results.

This project started by identifying premises in the RMEA and tracking the cattle using the Canadian Cattle Identification Agency (CCIA) tags issued to those premises until the tags are retired at slaughter or export.

“Only 50 per cent of them were found, indicating that there are serious problems with the traceability system, especially when it comes to accounting for the retirement and/or export of tags,” Preston says. “Recent funding announcements and projects in development have a strong focus on this problem because slaughter surveillance is critical to doing less herd testing and right now, we’re not getting the data.”

Of course, the producers have to be willing to share their premises ID and data in order to make this work. In February, people were already on the ground asking RMEA producers to sign off on sharing their testing information with MBP. Otherwise it remains confidential through an agreement between the CFIA and CCIA.

The Manitoba government has since committed $150,000 to back the development of a surveillance program using TB test results from packing plants and abattoirs for cattle originating in the RMEA. This project will be managed by the producer-run MBP. The federal government is also on board with $297,000 to support ongoing development of a disease-testing model, tracking TB test results at slaughter, and enhancing existing monitoring and management activities.

Beyond Surveillance

On-farm risk assessments coupled with biosecurity measures will be important in the effort to reduce the level of routine testing.

TB spreads through saliva, making saliva left on bales the most likely route of transmission from wildlife to cattle. Assistance has been available for building eight foot high stackyard fences. Now there is interest in 3D fencing to prevent mingling of cattle and wild cervids. (For more on 3D fencing, see Canadian Cattlemen, October 2013.)

A herd-health module has been developed to be delivered in conjunction with CFIA testing.

“There has been concern over the years that testing has a negative impact on some of these herds and we’ve been able to demonstrate that’s not the case,” Preston says. A third-party review of TB control programs in four other countries found no documented negative health effects from long-term repeated tuberculin testing. Negative effects on cattle and people due to stress have been documented and recognized, however.

The reviewer also found that research is underway to develop alternatives to the current TB-testing regime, including a vaccine, however, none are likely to be available any time soon and are possibly 10 years away.

Preston says a new surveillance model is being developed by the CFIA and MBP with input from AusVet, an Australian consulting company.

The current Manitoba project will provide useful information for other jurisdictions should they have to deal with TB issues down the road.

TB has been present in Canadian dairy and beef herds since 1897 when the federal government started providing free testing. Ten years later, TB inspections at packing plants were introduced. Area TB testing started in 1923 and outbreaks weren’t uncommon through to 1961, when the first general TB test was conducted across Canada. Approximately 400,000 of the 500 million cattle tested had positive reactions and were put down.

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