MRSA study sparks new questions about transmission

Tampa, Fla. — "Superbug," or methicillin-resistant Staphylococcus aureus (MRSA), infections are not a new concern for health-care professionals, including veterinarians. Community-acquired MRSA strains have been on the rise for the last decade, but more light is being shed on how these infections are being spread between people and their pets.

At risk: It's relatively easy for humans to transmit MRSA to their pets.

"I think there's an awareness for MRSA to occur in pets, but I think the idea in this country that pets can transmit back to humans isn't something that's always recognized," says Richard Oehler, MD, author of a new study on MRSA transmission.

There is an emerging problem in both veterinary and human medicine with cases of community-acquired MRSA involving the USA300 clone, Oehler, an infectious-disease specialist at the University of South Florida College of Medicine, says in the article he co-authored for a recent edition of The Lancet Infectious Diseases. His study focuses on various problems caused by animal bites but places extra focus on MRSA infections.

"My hope is that there's more education about the potential of MRSA in humans to be spread back to the veterinarian," he says, noting several cases of colonization among veterinary health professionals.

The tie is that humans can transmit MRSA to their pets — especially in cases of service dogs that visit hospital wards — which then transmit the infection back to humans.

The first confirmed case of USA300 community-acquired MRSA isolated from a household pet was in 2006, the study notes, while the first published case of domestic animal transmission of MRSA strains was in 1988 when a ward cat was believed to be the source of MRSA colonization in 38 percent of a geriatric unit's nursing staff. The outbreak came to a halt when infection-control measures were taken and the cat was removed from the hospital ward, Oehler adds.

Treatment on infections in animals with fluoroquinolones might contribute to the spread of fluoroquinolone-resistant MRSA strains in animals, which then can be transmitted to humans, he says.

The most important take-away, though, is that transmission is not just a one-way street, Oehler explains.

"The recognition of MRSA as being potentially associated with pets goes back several decades, but over the last five years there's been an increase in pets at the same time as USA300 or ST8 is increasing in humans," Oehler says. "The increase has happened simultaneously in pets and people, and this issue has become more pressing because we have a new superbug strain that's affecting both humans and their pets."

In humans, MRSA colonizes in nostrils. It's easy for humans to transmit their infection to their pets by having open wounds or not washing their hands frequently or before handling their pet. But exactly how MRSA infections transmit to pets is something that Oehler is not sure of.

"We don't exactly understand all the mechanisms by which transmission occurs," he says. "What interventions can reduce the risk? Do we decolonize our pets? There's a technique for eradicating colonization with antibiotics to rid the human body of staph. But is this an effective strategy in a household with multiple pets?"

These are the questions that have yet to be answered, Oehler says, noting that increased collaboration and shared research between human and animal medical professionals is key to finding the answers.

"This is something we both need to be aware of and work together on," Oehler says.