Methicillin-resistant Staphylococcus aureus (MRSA) is a nosocomial pathogen that has been recognized worldwide. Recently, a 3-year-old, neutered male domestic shorthair cat was presented to a specialty clinic with a 1-year history of multifocal patches of crusted and well-demarcated ulcers on the trunk. Initially the cat had been treated for flea allergy and pyoderma but had not responded. The owner reported the presence of skin abscesses and pneumonia 3 months earlier. Exudate from the cat's lesions had neutrophils and eosinophils with engulfed cocci. A CBC showed leukocytosis with eosinophilia. Histopathology showed a pattern of inflammation that may be associated with MRSA infection in cats. There were ulcers and dermal granulation tissue with linearly arranged eosinophils, mast cells, neutrophils, and plasma cells between dense homogeneous collagen bundles (sclerosing dermatitis). MRSA was isolated from the lesions. After identification, swabs of the anterior nares were collected from the owner and cat, and MRSA was isolated from both. Reports of MRSA infection in pets have increased dramatically in the past few years; however, this rise might be due in part to increased testing and reporting. Although the role of pets in transmission of MRSA is unclear, evidence suggests that MRSA can be transmitted between humans and their pets.

COMMENTARY: This same issue of Emerging Infectious Diseases reported on a survey that was conducted at an international veterinary conference (American College of Veterinary Internal Medicine Forum, 2005).1 Participants took their own nasal swab. MRSA was isolated from 6.5% of the attendees. Although no control group was evaluated, this prevalence is higher than previously reported rates for community-based colonization. A similar study in medical professionals at a conference reported a rate of only 0.3%. MRSA infection has been reported in cats, dogs, horses, birds, cattle, and pigs. It appears that MRSA is emerging as an important veterinary and zoonotic pathogen. The exact role of pets in the transmission and colonization of MRSA still needs to be evaluated, but veterinarians need to be aware of the increased risk for this infection.

1. Methicillin-resistant Staphylococcus aureus colonization in veterinary personnel. Hanselman BA, Sruth SA, Rousseau J, et al. Emerg Infect Dis 12:1933-1938, 2006.

Methicillin-resistant Staphylococcus aureus in cat and owner. Vitale CB, Goss TL, Weese JS. EMERG INFECT DIS 12:1998-2000, 2006.