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Antibiotic resistance in farm animals a growing concern for scientists


We’ve all heard about the growing threat of “superbugs,” or bacteria that have become resistant to the drugs we currently use to treat them. And we know that our sometimes inappropriate use of antibiotics shoulders much of the blame. The more bacteria are exposed to antibiotics, the more they develop ways to fight back. But what about all the antibiotics given to animals?

More than 75 per cent of all antibiotics used in Canada, by weight, go to farm animals, according to a report by Canada’s chief public health officer. That’s because a majority of antimicrobials are given on farms in a preventative, or prophylactic, way. Entire herds or flocks of animals are often given low doses of antibiotics to help them grow faster and prevent the infections that they would likely otherwise get.

Humans can pick up resistant bacteria through direct contact with animals and through eating improperly cooked meat that contains, for example, drug-resistant salmonella.

Studies at farms in the Netherlands and Ontario have found pig farm workers are many times more likely to be carrying Methicillin-Resistant Staphylococcus aureus (MRSA) than the general population. This drug-resistant bacterium is responsible for the deaths of more than 11,000 people each year in the US, according to the Centers for Disease Control and Prevention.

Data from the Canadian Integrated Program for Antimicrobial Resistance Surveillance (CIPARS) found the number of people infected with salmonella resistant to ceftiofur, a drug used in the poultry industry, correlated strongly with the use of that drug on Quebec farms in the early 2000s. Ceftiofur-resistant salmonella is also likely to be resistant to ceftriaxone, the “drug of choice” for treating extra-intestinal salmonella infections in children and pregnant women, according to the Public Health Agency of Canada.

John Prescott, co-chair of the Ad-Hoc Committee for Antimicrobial Stewardship in Canadian Agriculture and Veterinary Medicine is quick to point out, however, that the overuse of antibiotics in people, not animals, “is what’s driving the antibiotic resistance crisis.” And most scientists agree. In a well-cited survey of UK infectious disease experts, respondents estimated agriculture’s contribution to antibiotic resistance in humans is less than two per cent.

Others think the risk to human health is far underestimated. Dr. Stuart Levy, director of the Centre for Adaptation Genetics and Drug Resistance at Tufts University in Massachusetts, argues such low estimates discount the indirect ways drug-resistant genes can move from animal to  human bacteria. Lab studies by Levy and others have shown bacteria of very different types swap resistant genes with each other. “You take the feces from animals and put it as fertilizer on soils where you’re growing fruits and vegetables,” he says. “And we know that resistant genes don’t stay where they are, they move and become different.”

The animal-to-human movement of resistant genes through the food chain is very difficult to prove, however, in part due to various mutations along the way. For example, a recent study arguing that drug-resistant urinary tract infections in women are caused by the consumption of drug-resistant E. Coli in chicken has been met with controversy; some scientists argue that because resistant bacteria in chickens and people are genetically similar doesn’t prove it transferred from animals to humans.

Canada not doing enough to limit antibiotics on farms

Regardless of how they characterize the threat posed by animal antibiotic resistance to humans, all the experts we spoke to argued that Canada needs to do more to regulate antibiotics in agriculture.

“Agriculture has got to step up to the plate,” says John Prescott, co-chair of the Ad-Hoc Committee for Antimicrobial Stewardship in Canadian Agriculture and Veterinary Medicine. “We’ve got to be using antibiotics better, using antibiotics less and measuring what antibiotics are being used and why they’re being used.”

Last year, Health Canada announced significant policy changes that aim to better control antibiotic use in food animal production. By December 2016, antibiotics can no longer be given to promote growth in animals. (Although the growth-promoting benefit of antibiotics is smaller than previously thought “it’s hard to buy pig feed without antibiotics in it,” says Prescott, who calls the new Health Canada rules a “game changer.”) In addition, antibiotic-containing feed and water – which currently doesn’t require a prescription – will need to come under “veterinary oversight.”

What that oversight entails is still being discussed, according to Eric Morrissette, a Health Canada spokesperson. Several sources argued, however, that the policy should ensure veterinary oversight isn’t undermined by conflict of interest. Given that many vets both prescribe and sell drugs, one way to address this conflict is to “partition” prescribing and selling roles, says Lynora Saxinger, an infectious disease specialist at the University of Alberta.

Meanwhile, everyone we spoke to argued that veterinary oversight will be severely limited if legal loopholes that allow farmers to directly import pharmaceutical drugs and pharmaceutical ingredients aren’t closed. Currently, farmers can bring in antibiotic drugs from abroad and feed them to animals without any veterinarian or government official knowing what’s being given, or why. “You can order bulk chemicals, bring them in and mix up your own mix and feed it to livestock and there’s no regulatory control over that,” explains Skippon.

The first advisory committee convened by Health Canada on antimicrobial resistance on farms, in 2002, recommended the loopholes be closed, but they remain to this day. “There’s been a lot of push back from industry stakeholders,” says Skippon, pointing out the loopholes allow farmers to access medicines more cheaply.

Others think that while closing importation loopholes and bringing in oversight is an important step, the entire mindset of veterinary medicine needs to change. “We might just end up creating a semantic change,” says Patrick of the ban on the use of antibiotics for growth purposes. “It’s quite possible you’ll still see widespread use of antibiotics in feed in the name of prophylaxis.”

And as with antibiotics used for growth, the low-level and longer-term use of preventative antibiotics is more likely to lead to resistance than antibiotics given for short-term treatment purposes.

But Warren Skippon, manager of animal welfare at the Canadian Veterinary Medical Association says that, often, giving preventative antibiotics can “minimize the amount of drugs that may be needed for treatment purposes” and prevent bacterial infection in an end product. On conventional dairy farms, an antibiotic is given to cows after they stop producing milk, for example. The drug is out of a cow’s system by the time she’s producing milk again, but decreases the need to treat infections at that time, Skippon explains.

Stephanie Brown, director of the Canadian Coalition for Farm Animals, argues, meanwhile, that preventative antibiotics wouldn’t be so often required for chickens, pigs and cattle if modern agriculture wasn’t about “raising the largest animals in the shortest time with the least amount of food in the smallest space.”

The Ontario Medical Association also doesn’t think that routine use of preventative antibiotics is necessary in agriculture, and has called for a ban on the practice. Other jurisdictions show it’s possible to dramatically curtail prophylactic use. In the 1990s, Sweden banned all prophylactic use of antimicrobials on farms and Denmark banned routine prophylactic use. Swedish farms have reduced prophylactic antibiotic use three-fold since 1986, a reduction believed to be made possible by the introduction of strict requirements limiting density of animals and improved animal welfare standards on farms.

Health Canada recommends against the animal prophylactic use of cephalosporins, which are antibiotics that are critically important in human medicine. Two years ago, the U.S. Food and Drug Administration went a step further and banned the preventative and off-label farm use of cephalosporins. But Morrisette at Health Canada claims the body can’t ban such use because the federal government regulates whether or not a drug can be sold in Canada, while provinces regulate how the drugs are to be used.

For Prescott, that’s “nonsense.” Canada has a federal agency  – CIPARS – that samples animals, humans and meat when there is concern about resistant bacterial infections spreading from farms to animals. So it should be up to the federal government to respond if its own data show a dangerous resistant bug is spreading among animals and people, Prescott argues.

“If suddenly we’re seeing lots of third-generation cephalosporin resistance in salmonella carried by chickens and it’s causing disease in people …then we believe Health Canada can’t just throw up its hands and say ‘Oh well, use is provincial.’ They should be able to intervene and say it is now illegal to use third generation cephalosporin in chickens,” says Prescott. “What’s the point of having an organization like CIPARS if you can’t do anything about its findings?”

In light of little federal action on agricultural antibiotic regulation, Patrick thinks change will come not from industry or government, but consumers calling for reduced usage of antibiotics in food animals. “What’s going to drive this far more than me nagging from the health care sidelines is consumers being clear with producers about what they expect about the product they bring home.”

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  1. David Alves DVM PhD

    This article is reasonably well written however leaves the reader confused on the path forward with this important topic of antibiotic resistant. The science and endless debate from academics and others is confusing – but what gets lost is that the solution is very very clear. Reduce the amount of antibiotics used in all species – especially those in agriculture as soon as possible. The human field has come a long way in this regard. Now we know that over 70% of all antibiotics in North America are used on animals (even with some common animal growth enhancing chemicals removed from the figures due to academic debate about their role in all this). Agriculture should be given a fair chance to put voluntary measures and education in place for their organizations and producers. If after 5 years they have not shown at least a 30% reduction in the amounts of antimicrobials used – then all levels of government can easily bring in regulatory controls. Often forgotten is that this is an important health issue to all of the public – those who eat North American meat and vegetables and those that do not. Resistance genes are shared widely among the flora and fauna. The solution is just to reduce the high amounts of antibiotics used in all species as soon as possible.

    • Punkinhead

      Would this also then entail improvements in animal welfare? Factory farming depends on AMs, and happy animals are healthy animals, with strong immune systems and healthy guts? I have a whole discussion paper on this if you’d like to write to me privately.

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