The threat of antibiotic resistance looms large for veterinarians. Dr. J. Scott Weese, an infectious disease specialist and veterinarian at Ontario Veterinary College, knows this better than most.
Weese says veterinarians have always been aware of the intersections between human and animal health. As the list of antimicrobial-resistant diseases continues to grow, Weese and others in the veterinary community have been active in identifying strategies to prevent the spread. “Now more than ever, veterinarians are integral to protecting animals and our public health,” he says.
Antibiotic-resistant infections threaten both humans and animals. A recent global study reported that antibiotic resistance contributed to nearly 5 million human deaths in 2019. Two of the deadliest pathogens identified, Escherichia coli and Staphylococcus aureus, are among several shared between animals and humans. While there is less data available on the prevalence of resistant infections in animals, antibiotic-resistant pathogens have been documented in dogs, cats, cows, chickens, horses, sheep, pigs, and others. When animals or humans have been previously or repeatedly treated with antibiotics, resistant bacterial populations are more likely to develop.
For veterinarians, addressing antibiotic resistance requires a multifactorial approach that both acknowledges veterinary medicine’s contribution to the problem and considers the extrinsic factors that have led to the spread of resistance. Overprescribing of medications is targeted, justifiably, in both the human and veterinary medical professions. However, Weese points out the situation is more nuanced.
“It’s a complex ecological problem,” he says, “and it requires a complex solution.”
Key to this complex solution is implementing strategies like the judicious use of antibiotics and good infection control measures–actions that veterinarians can control in their clinics or hospitals. But veterinarians, with their knowledge and expertise, are also uniquely poised to confront some of the wider issues leading to antibiotic resistance, including how companion animals are bred and how farmed animals are treated.
Companion animals and antibiotic resistance
Drug-resistant infections have risen in companion animals over the past several years, and resistant skin, urinary tract, and surgical site infections are of increasing concern. Dogs and cats can carry methicillin-resistant Staphylococcus aureus (MRSA) that they likely first acquired from people, and the risk of passing it to humans is low. Of greater concern, says Weese, are the drug-resistant gram-negative bacteria like E. coli and Salmonella that can colonize the gastrointestinal and urinary tracts of dogs and cats and cause severe illness and death in people. One study found that antibiotic-resistant E. coli detected in urine samples from dogs increased by over 30 percent from 2010 to 2017.
Unnecessary antibiotic prescriptions are a driving factor in bacterial resistance in pets, and there are a variety of reasons why a veterinarian may inappropriately prescribe an antibiotic. Veterinarians may be faced with limited diagnostic options due to client financial constraints. According to Weese, they may be worried about missing something or concerned about client dissatisfaction when an animal doesn’t get better quickly. There’s often an expectation from animal caretakers that they should receive antibiotics for their pets and a lack of understanding when they don’t. Common situations like these may also lead veterinarians to default to longer antibiotic durations than necessary, another practice that could lead to resistance.
However, Weese points out that other important factors contribute to drug resistance in pets, and this entails taking a critical look at how animals are bred and fed.
For instance, the trend to feed raw meat diets to dogs and cats may have driven antibiotic resistance by exposing pets and people to resistant bacteria in farmed animals. As early as 2008, Weese published research showing a connection between raw diets fed to dogs and drug-resistant E. coli detected in their feces. Since that time, many studies have corroborated these findings in dogs and cats.
There’s also a range of issues pertaining to how companion animals are bred. Breeding for certain characteristics, like the compressed noses of pugs and bulldogs, presents significant welfare concerns for animals along with higher infection risks. Other breeds, predisposed to skin diseases, may require repeated and prolonged courses of antibiotics. “A massive amount of antibiotic use could be controlled by better management of some of these breeds that end up being medical disasters–dogs with allergic skin disease, dogs always getting respiratory diseases,” says Weese.
Antibiotics and farmed animals
Non-judicious antibiotic use in farmed animals who enter the food system is a significant source of concern. Common antibiotic uses in farmed animals differ from companion animal uses in critical ways. Farmed animals are more likely to be given antibiotics prophylactically as disease prevention within a herd or flock before any signs of illness. If some animals are sick, all exposed animals may be treated regardless of whether they are ill, an approach called metaphylaxis. Although these approaches may sometimes be used in pets, they predominate in farmed animal medicine. Farmed animals may also be treated individually at times for infections and illnesses.
For decades, farmed animals were given subtherapeutic doses of antibiotics, called growth promoters, in their food and water. This practice likely significantly advanced the development of antibiotic-resistant populations. As animals were exposed to antibiotics, bacteria in their gastrointestinal tracts acquired resistance. People, in turn, came into contact with these resistant bacteria when they handled and consumed the animals.
Until 2017, the use of growth promoters was controlled by farmers since the antibiotics used didn’t require a veterinary prescription. That changed when the U.S. Food and Drug Administration (FDA) implemented the Veterinary Feed Directive, effectively banning growth promoters and placing antibiotics under veterinary oversight.
Weese says this move has given veterinarians a chance to be more hands-on. “We’ve never been complete gatekeepers of antimicrobials when it comes to animals, but there’s movement towards that.”
The question remains what veterinarians may do with this opportunity to take better control of antibiotics in animal agriculture. After a drop in antibiotic use in 2017, the FDA reported an eight percent increase in 2020. The very nature of intensive animal agriculture–which confines animals in crowded, stressful spaces conducive to disease spread–is predicated on the frequent use of antibiotics. Veterinarians can play a role in addressing this, but it must be done on a systemic level.
“If you try to over-intensify, you run into problems,” Weese says. “Antibiotics become a crutch.”
But he doesn’t see intensive agriculture itself as an insurmountable problem, and believes veterinarians can work with producers to improve systems. “We need to optimize animal health for animal welfare, for food safety, and for antimicrobial use,” he says. “We need to focus less on intensification and more on animal handling, housing, and health systems.”
A complex solution
While the Veterinary Feed Directive gave veterinarians better control, there are groups that feel this regulation didn’t go far enough to curtail antibiotics in animals. But Weese thinks it’s better if initiatives for judicious antibiotic use originate from the veterinary community. “Regulatory approaches sometimes lead to unintended negative consequences on our ability to treat patients–the banning of label use of certain drugs means that sometimes drugs have to be used suboptimally,” he says. This affects veterinary patient health.
According to the American Veterinary Medical Association, veterinarians can address issues like overuse by committing to antimicrobial stewardship principles. These include educating people about preventative care to avoid the need for antibiotics, teaching and practicing judicious antibiotic use based on diagnostics and evidence, and implementing rigorous hygiene, husbandry, and infection control measures.
As Weese says, antibiotic resistance requires an expansive approach that recognizes the many connections between animal and human health. This applies in a broader sense to how animals are treated. Veterinarians can play an important role in tackling some of the root causes of antibiotic resistance.
“We can’t give antibiotics to compensate for poor practices,” he says. “If we address proper animal care, then those antibiotics will be available when we really need them.”
Ingrid L. Taylor is a writer, poet, and veterinarian whose work explores strategies for fostering multispecies solidarity and deconstructing speciesism. She has worked in clinical veterinary medicine and public health.