Going to the Dogs: Pets and Owners Share Resistant Pathogens

Daniel M. Keller, PhD

September 28, 2011

September 28, 2011 (Chicago, Illinois) — The gastrointestinal tract of dogs might be a reservoir of fluoroquinolone-resistant extra-intestinal pathogenic Escherichia coli (ExPEC), which is a public health concern and includes the 025b-ST131 (ST131) strains that have been associated with human extra-intestinal infections.

That is what Siyu Guo, a doctoral student in the School of Veterinary Science at the University of Queensland in Gatton, Australia, told delegates here at the 51st Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC).

From March to September 2009, the investigators screened the feces of dogs hospitalized in a major Australian small-animal veterinary hospital for fluoroquinolone-resistant E coli. For all isolates found to be resistant to both ciprofloxacin and pradafloxacin, researchers performed phylogenetic grouping and virulence profiling for 33 virulence factors associated with ExPEC.

They found that several strains of E coli from people and dogs were genetically closely related. Of 124 dogs tested, 68% yielded E coli resistant to ciprofloxacin (≥0.25 μg/mL) and 18.5% yielded E coli resistant to ciprofloxacin and pradafloxacin. Two dogs yielded 30 ciprofloxacin/pradafloxacin-resistant ST131 isolates with 3 distinct virulence factor profiles, including those previously reported in human ST131 strains. Since it was first recognized in 2008, ST131 has been found globally among human populations, and causes extra-intestinal infections.

The authors noted that "from a microbiological point of view, dogs are truly a part of the family," citing previous reports showing that a strain of E coli causing urinary tract infections in people could be shared back and forth between human and canine household members.

Such transmission implicates dogs as a part of the epidemiology of extra-intestinal E coli; they might be a reservoir of resistant bacteria in households experiencing recurrent E coli urinary tract infections. However, the investigators noted that only 2 of 124 dogs in this study carried ST131, so they are probably not a major vector for disseminating this strain on a global level. In fact, "the major direction of transfer...could be from humans to dogs," they said.

Jesús Rodriguez-Baño, MD, PhD, head of infectious diseases at University Hospital Macarena in Seville, Spain, told Medscape Medical News that several studies have shown that owners and pets share some bacteria and some resistance genes. "We don't understand very well how important pets are in the maintenance as a reservoir, as a transmitter of some resistance genes, but actually, there are increasing data suggesting that they might be as relevant as other members of the family," he said.

Lindsay Grayson, MD, MSc, professor of medicine at the University of Melbourne in Australia, and chair of the ICAAC program committee, agreed. "If I look at my kids, they're cuddling the dog more than they cuddle me half the time. It's only natural that if those animals have bugs, they could spread them," he said.

Transmission of bacteria and viruses between people and animals is a 2-way street, Dr. Grayson told Medscape Medical News. He referred to studies showing that people have spread methicillin-resistant Staphylococcus aureus to their pets, and reported cases in which pets have come back from a veterinary hospital and spread the bacterium to their owners.

Another aspect of the problem is that antibiotic use in pets and in farm animals is not as strictly regulated as it is for people. "Whether you're a dog or a human, those same principles apply," Dr. Grayson emphasized. "If you are misusing antibiotics, it will lead to the emergence of resistance."

He noted that some studies have looked at whether it would be appropriate to treat a pet if a person has recurrent infections. He said there are interesting data from the Netherlands showing that when some pig farmers had recurrent infections, the same strain of bacterium was found in the pigs.

The question of treating animals is particularly relevant in the case of a person who is immunosuppressed and gets recurrent infections with a certain organism. "Then pets are on the agenda.... You have to worry about whether the environment is contaminated or whether their medicines are working properly," Dr. Grayson said.

Whether pathogens will adapt to both human and animal reservoirs depends on how close the reservoirs are immunologically. "That's why pigs are so important.... Immunologically, they're similar, so the movement of bugs, whether it's influenza or staph, is easier," he said. "In other species, like cats or dogs, it's further distant from humans, so it's rarer for the same bug to be infecting both."

Dr. Grayson said the message to veterinarians and to physicians is the same — "wise antibiotic use, [and] only use it when you need to."

The study was funded through an Australian federal government research grant in cooperation with Bayer Animal Health. Guo reports receiving funding from Bayer Animal Health. Dr. Rodriguez-Baño and Dr. Grayson have disclosed no relevant financial relationships.

51st Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC): Abstract C1-472. Presented September 18, 2011.

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