Battling bovine tuberculosis

Canadian researchers are working on TB vaccines and developing strategies to manage the disease in wild animals

Research is underway in Canada to develop a vaccine aimed at eliminating the threat of bovine tuberculosis (TB). If successful, the results will mean better health for cattle and humans around the world.

Dr. Jeff Chen and his colleagues are researching TB and developing vaccines to combat the disease.
photo: Debra Marshall

“When we say bovine TB, sometimes it can also be TB that’s found in humans,” says Dr. Jeff Chen, explaining that Mycobacterium bovis (M. bovis) is part of a large family of closely related bacteria, which includes the bacteria that causes TB in humans.

Chen leads the Mycobacterial Pathogenesis and Tuberculosis Research Program at the University of Saskatchewan’s Vaccine and Infectious Disease Organization-International Vaccine Centre (VIDO-InterVac).

He says that because there are potential human applications, investment in developing the vaccine to safeguard the cattle industry will also help in the fight against human TB.

According to the World Health Organization, TB in humans has surpassed HIV/AIDS as the world’s number one killer due a single infectious agent. An estimated 10 million people were infected as of 2018.

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Disease transmission and control

It can also affect other species such as sheep, goats and even family pets. It even makes its way into wildlife populations, which is why it’s so difficult to eradicate.

In the U.K., the practice of culling wild badgers to contain the spread of bovine TB in domestic cow herds has caused public controversy and division for decades.

“In most industrial nations, the way you deal with an outbreak is to test, identify animals that are infected and then cull them,” Chen says. But if healthy cows pick up the bacteria from wildlife, culling is not an effective control method.

“The fact that it’s spread through the air, affects so many different species and it is able to persist in wildlife reservoirs makes it a tough disease to deal with,” he says.

In Canada, Dr. Todd Shury has had success reducing bovine TB in a deer and elk reservoir deep in the farmland of southern Manitoba.

Dr. Todd Shury.
photo: Lana Height

“It took 15 years of concerted effort, but we reduced the incidents of infection from about 10 per cent to near zero in Riding Mountain National Park,” says Shury, who’s the national wildlife health advisor in the Office of the Chief Ecosystem Scientist with Parks Canada. Shury is also an adjunct professor in the Western College of Veterinary Medicine at the University of Saskatchewan. The project was a joint effort of the federal and provincial governments, the Canadian Food Inspection Agency (CFIA), the cattle industry and others.

He’s now working on research to find a way to manage bovine TB in wild bison herds. Preliminary laboratory work has been completed, and in January 2020, the first trial will begin with bison. The goal is to try to manage the disease in the herds in and around Wood Buffalo National Park, which straddles northern Alberta and the Northwest Territories. There, brucellosis and bovine TB have been present since the 1920s, when some infected Plains bison were shipped into the area.

As far as cattle goes, Canada, for now, is considered a bovine TB-free country. But problems have arisen as recently as 2016 in Alberta, when six cases were found in cattle on a single farm, and when four cases were detected in 2018 in British Columbia.

“For trade purposes, it’s very important that we retain our disease-free status,” Chen says, adding that the federal government and industry are keen on staying that way.

High-security laboratory

At the time, the laboratory had just received regulatory approval to work with the highly contagious pathogen.

“We use very strict rules and procedures,” he says. Since his arrival, the research has centred on basic research into the disease, developing better models of how the disease behaves in cattle, using swine to mimic how the disease is transmitted and progresses in humans, and developing the actual vaccines.

“We have several vaccine candidates, including a sub-unit protein candidate and a live vaccine candidate,” he says. Both types of vaccines prepare the immune system to fight infection in different ways.

Chen is cautiously optimistic that the couple of vaccines under development now will be ready in two to three years’ time for clinical trials.

“It’ll be roughly another five to six years after that before we have something that’s commercially viable for veterinary use,” he says, adding that the candidates they are working on could eventually be used for both bovine and human TB.

Two of the main principles when developing any type of vaccine are efficacy and safety.

“It has to work and it has to be very, very safe,” he says, particularly for vaccines that are involved in the food system. The process for bringing vaccines to market is rigorous, through proof of concept testing, efficacy testing and safety testing.

The attrition rate is substantial — a field of 10 candidates can be winnowed down to one or two.

Challenges beyond developing the vaccine

“It’s really important for industry stakeholders to know this, and to help move things into the market,” Chen says.

In Canada, he says, the CFIA has strict protocols to keep Canadian herds healthy and free of disease from foreign countries.

“We have great systems in place — surveillance is really good, detection is there, testing takes place and culling happens quickly.”

Despite this, he believes that we need to keep working to find ways to prevent the disease from occurring in the first place.

“It’d help if our global partners could benefit from this research as well,” he says. “In developing nations, they can’t afford the test-and-cull system that we have.”

Besides the economics, he says that in some countries, it’s not feasible for social and cultural reasons as well.

Because bovine TB is a chronic disease and symptoms may persist over time, farmers who can’t afford to cull them could continue milking and even breeding infected animals.

“In situations like this, a vaccine would be the best bet,” he says.

About the author

Contributor

Lois Harris is an experienced Ontario freelance writer and editor working in the agriculture and food industry.

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