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The widespread use of antibiotics in livestock feed is creating superbugs that are spreading off farms and endangering human health, a B.C. doctor says.

Dr. Bill Mackie, chair of the B.C. Medical Association's environmental health committee, says antibiotic-resistant strains of bacteria developing in livestock pose a real risk to humans.

"It's a big issue. I seriously worry about the day when none of the antibiotics we have access to is going to treat those infections effectively," he said.

Antibiotic resistance develops in bacteria when the drugs kill most — but not all — of the germs, leaving only those with mutations that allow them to survive and propagate as a new strain that antibiotics can't destroy.

Scientific studies have found resistant strains of bacteria in meat on Canadian store shelves and in the environment near farms, including those in the Fraser Valley, east of Vancouver.

Daily dose for chickens

Abbotsford farmer Rick Thiessen initially told CBC News he only uses antibiotics on his farm when there's a rare outbreak in one of his barns.

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Dr. Bill Mackie says the use of antibiotics in livestock is endangering human health. ((CBC))

"Antibiotics will be used if you're finding a problem with your flock. You consult a veterinarian, have a diagnosis, he prescribes a course of medication and we'd use them in that sort of instance. But to be quite honest, I can't remember the last time we've had to do that," said Thiessen.

But after repeated questions, Thiessen, who also speaks for the B.C. Chicken Marketing Board, said his chickens eat feed fortified with an antibiotic called Tylosin every day to prevent illness.

"Chicken, by nature, have bacteria in their gut tract and, in order to keep them healthy, there are approved products that are used in the feed," he said.

Thiessen said with 20,000 chickens running around in each of his barns, they'll occasionally peck at their own manure, which could make them sick without the antibiotic.

Growing use questioned

There are more than a dozen antibiotics approved for livestock feed in Canada, falling into three main categories: to treat illness, to prevent illness, or to help the animal grow faster.

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Bob Hancock says research has shown antibiotic resistance is growing because of the widespread use in livestock. ((CBC))

It's that last category that's most controversial. Europe for example, banned the use of antibiotics to promote livestock growth years ago.

The Animal Nutrition Association of Canada, an industry group representing feed manufacturers, is adamant they use them to prevent illness but not for growth promotion.

But Bob Hancock, director of the Centre for Microbial Diseases and Host Defence Research at the University of British Columbia, argues that prevention and growth promotion are the same thing.

The reason antibiotics work to speed up growth is that they fend off illness, taking some burden off the animal's immune system so more energy goes into putting on weight, he says. But this short-term gain of more meat has the long-term cost of drug-resistant bacteria.

"There's no question in my mind that growth promotion provides a massive pressure leading to increased antibiotics resistance," said Hancock.

Affecting human treatments

According to Hancock, Tylosin is just one of many drugs that can make bacteria resistant to a whole class of antibiotics used in human medicine.

"There are some very potent antibiotics, erythromycin, clarithromycin, all of which are utilized very highly in critical-care human medicine, and all of which — when you make organisms resistant to Tylosin — they become resistant to these other potent human antibiotics. And it goes on," said Hancock.

A study published this year in the journal Emerging Infectious Diseases, by researchers from the Public Health Agency of Canada and the B.C. Centre for Disease Control, found a specific resistant strain of Salmonella in humans, including B.C. patients, that matched what's found in chickens.

"The organisms that come from that can end up in people and, therefore, can affect the treatment of people afterwards because the antibiotics that previously would have cured that particular organism now would no longer be effective," according to Mackie.

Resistant strains can be difficult and more expensive to treat, and that has led both the B.C. Medical Association and Canadian Medical Association to call on the government to investigate.

Health Canada declined CBC's request for an interview, but Mackie said it is time for the government to act before the health impacts become more widespread.

"What we have to do as a society is stand up and say this is going to make us sick. This is going to make my kids sick, if it continues, my grandkids are going to be sick all the time. There has to be some digging in. We have to make some changes," he said.