Canadian livestock consume more than 1.6 million kilograms of antibiotics every year, according to the Canadian Animal Health Institute. But what are the effects of those antibiotics on the human body? Public health experts say the use of antimicrobials in food animals could have serious implications on our overall health and future resistance to infectious disease.
The long-term effects of antibiotics and antibiotic resistance on the human body are drastically under-studied both in Canada and worldwide. Only in the past decade have researchers begun looking at the effects antibiotics and antibiotic-resistance bugs have on the human “microbiome.”
The microbiome is a universe of bacteria and other tiny organisms that live in and on us. This complex and fragile system is essential to human health; we’re still learning what effect antibiotics have on it.
“We need these microbes to help us digest food, to protect us from pathogens and all sorts of things,” says Gerry Wright, Director of McMaster University’s Michael G. DeGroote Institute for Infectious Disease Research and Professor of Biochemistry and Biomedical Sciences.
“So when you take an antibiotic … you immediately have an impact on those microbes because they’re equally as susceptible to antibiotics as the ones causing the disease.”
Wright said some people never regain the old versions of their gut microbes that they had before they took the drugs.
“One of the side effects that you hear about from all antibiotics is that it may cause diarrhea – well that’s why it’s causing diarrhea it’s because it’s killing off all of those microbes that are normally there and it’s causing all sorts of hell to happen to your gut,” he said.
But far more troubling is what the antibiotics doesn’t kill off: Wright said people who take antibiotics may end up with a “reservoir of resistance genes” in their stomach that could last for a very significant time period. It’s the rise of these drug-resistant bacteria that concerns public health officials, because they’re immune to our best mechanisms of combating them.
History of antibiotic use
The widespread use of antibiotics in North America came into effect after the large scale development of penicillin in the early 1940s. Within just a few years, antibiotics such as tetracyclines, macrolides, chloramphenicol, and streptomycin came into medical use to cure formerly fatal bacterial infections.
In the late 1940s, farmers discovered they could add antibiotics in low doses to farm animal feed to promote growth. Although it wasn’t well studied at the time, the cost-effective way of promoting growth in animals with minimal feed in a wide variety of species such as chickens, swine and cattle was seen as a godsend. An estimated 70 per cent of all antibiotics produced in the U.S. were used for the growth promotion of farm animals, according to a 2005 U.S. study on antibiotic growth promoters.
Today, about 80 per cent of the antibiotics consumed in Canada are destined for livestock.
The use of antimicrobials on animals to prevent illness has come under attack amid growing concern over the potential drug-resistant bacteria the practice creates, and the threat those bugs pose to both animals and humans.
For that reason, antibiotic claims of growth promotion have been banned in much of Europe. The U.S. and Canada are phasing out growth promotion use over the next 18 months.
Antibiotics used in Canadian livestock production
Canadian Animal Health Institute President Jean Skotnicki says 70 per cent of the antibiotics used on animals in Canada aren’t for growth promotion. And her institute is working to bring them all under veterinary oversight by the end of next year.
“We want to keep the medications useful for as long as possible. That makes good business sense. But we’re all people with families and we want to make sure that we can treat humans,” she said.
“I think in a lot of ways, healthy animals equate with healthy people because many of the diseases in the world are animal-derived. …
“So we really do want to keep our animals healthy, from an animal welfare standpoint and from a human healthfulness standpoint.”
The fear of antibiotic over-exposure
Martin Blaser, Professor of Internal Medicine and Microbiology at the New York University School of Medicine, has researched the effects of antibiotics on microbiomes. If the exposure of young animals to antibiotics alters their metabolism and development, he reasons, what are the effects of all the antibiotics given to human children?
Blaser cites an “enormous over-usage” of antibiotics in young children. There has been progress in recent years to curb this usage, he says, but exposure has been significant.
Surveys in the United States and in Europe have estimated that the average child receives 10 to 20 courses of antibiotics before the age of 18. Much of this exposure is during the first five years of life.
“We’re seeing that there’s this really intricate link between the bacteria that live in and on us and all the other systems that we need; respiratory system, nervous system, endocrine system,” Wright said.
“There’s an impact that we never really appreciated before.”
Wright runs a germ-free facility at McMaster to test hypotheses on animals that lack a microbiome, so the effects on animals can be studied.
The Canadian Institute of Health Research is also undertaking this task by studying the effects of antibiotics on microbiomes. But Wright said they are “insanely underfunded,” undermining their ability to do proper research.
“The impact of the kind of science that we can do in Canada is minimal, simply because there’s no investment in fundamental research in this country to make this happen,” he said.
“It’s a damn shame.”