Q: I was wondering about the spread of methicillin-resistant Staphylococcus aureus (MRSA) and pets. I have a 6-month-old male cat with swollen glands under his jaw. His ears and skin near his chin and mouth seemed to be really red, and he seemed to be itchy. He had a slight fever and a red sore under his armpit. I was told to give him an antibiotic, Clavamox. The bloodwork showed a high white blood cell count. He seems to be OK -- he's eating and running around -- but the sore concerns me. His temperature is now normal, but his glands are still swollen. Is there a definitive test for MRSA in pets?

A: MRSA is an up-and-coming issue in veterinary medicine, according to Dr. David White, director of the National Antimicrobial Resistance Monitoring System at the U.S. Food and Drug Administration's Center for Veterinary Medicine. MRSA was first reported in 1961, soon after the antimicrobial methicillin was introduced into human medicine to treat penicillin-resistant staphylococci, White explains via e-mail.

"MRSA has since emerged as an important human pathogen worldwide, and more recently, there is concern in the veterinary medicine and food safety arenas with regards to MRSA as a possible disease transmitted between animals and people," he writes.

White reports that MRSA infections in domestic animals have been reported among horses, pigs, cattle, sheep, cats, dogs and rabbits, as well as being reported as an emerging problem in veterinary teaching facilities.

Both human-to-animal and animal-to-human transmission of MRSA are known to be possible. However, it has not yet been adequately determined whether animals are an important primary source of MRSA infections for humans, or if most animals are infected after contact with human carriers.

Now about your cat with swollen glands and the sore under his armpit. "We routinely culture patients we suspect have underlying bacterial infections, and microbiologists will identify MRSA," writes Dr. Marc Elie via e-mail, a board-certified specialist in veterinary internal medicine at Michigan Veterinary Specialists.

Dr. Elie suspects your cat had some sort of allergic reaction rather than an underlying infection, since you are describing extreme redness of the skin rather than sores (with the exception of a single armpit sore). The glandular enlargement and high white blood cell counts may merely be a systemic extension of the allergic inflammatory response. Alternatively, the cat may have prominent salivary glands that are being misidentified as swollen glands.

Dr. Elie suspects your cat improved not because he received Clavamox, but rather because his allergic reaction coincidentally waned with time.

"To answer the question simply, it may be appropriate to biopsy the lesion under the armpit and submit it for both histopathologic analysis and bacterial culture," writes Dr. Elie.

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