Methicillin-Resistant Staph Bacteria Passed From Humans to Horses

"What do animal diseases have to do with people?" posed Scott Weese, DVM, DVSc, Dipl. ACVIM, an associate professor at the University of Guelph's Ontario Veterinary College. "We are just one big global population with subsets," he answered. Weese discussed methicillin-resistant Staphylococcus aureus (MRSA), a multi-drug-resistant bacterium that affects humans and horses. He said that one of the leading causes of hospital-acquired infections in humans is “superbugs like this. MRSA infections have recently begun spilling over into the community, spreading outside of hospitals as well.

Weese spoke during the "Cutting Edge of Animal Health" series of internal medicine topics presented to the press on June 2 at the annual meeting of the American College of Veterinary Internal Medicine (ACVIM) in Baltimore, Md. Weese has focused his research on MRSA infections for several years, learning how this and similar "superbugs" work and the best ways to eradicate them.

Antibiotic-resistant infections in horses are not simply a direct spillover from humans. Some of these "bugs" have adapted over time to more effectively infect the horse's body. A veterinary hospital employee can bring an MRSA infection to work (such as in his nasal passages), then pass it on unknowingly to an immune-compromised equine patient, who can then pass it on to other horses or humans.

The prevalence of MRSA is a concern because of the problems it's already causing at hospitals and because of the problems that it's likely to cause if veterinarians aren't aware of it. "There's no organization tracking it (in horses) in the United States, no mandate for physicians to follow up, and not all diagnostic labs are looking for it," he said.

MRSA infections are especially dangerous in equine hospitals as horses often are admitted with open wounds or they have had surgery, leaving them more vulnerable. "Post-operative (MRSA infections) can be fatal," explained Weese.

He's not sure why horses are so susceptible to these infections, why one uncommon human strain appears to have adapted to horses, or why this strain is not identified as a problem in small animals. Weese presented an abstract at the conference showing that MRSA was isolated from 5.3% of referrals to the Ontario Veterinary College's hospital. At the referral center, every horse is tested when it arrives.

"There's no solid evidence on what we should do to manage MRSA infections--in the hospital setting we isolate the individual (horse) in the clinic and handle it with gloves, gowns, and disinfection protocols  (Proper disinfection techniques with most standard hospital disinfectants should work)," he explained. "It gets a little more difficult in households (in talking about small animal care, or private barns)." He said many referral clinics are starting to test horses upon admittance.

At the ACVIM meeting, Weese and colleagues had a table where a graduate student was collecting surveys and nasal swabs from attending veterinarians. "We want to see what percentage of veterinarians are carrying it, and determine the risk factors (in terms of exposing horses and other staff)," he said. More than 300 people complied the first day. "We're going to take 500 swabs and compare (isolates) to common animal and human strains," he added.

Weese said that the quest to understand MRSA infections better is a fine example of a link between the human and veterinary sides of medicine.

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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