Where Do MRSA Infections Come From?

With recent news stories about the three Tampa Bay Buccaneer football players who were diagnosed with MRSA, questions regarding these types of infections in pets are likely to arise.

MRSA is short for Methicillin-Resistant Staphylococcus aureus. Staph aureus is a type of bacteria found in the nasal passages of up to 30-40 percent of healthy people. It can also be found anywhere on the skin, in soft tissues, or in the ears. It usually doesn’t cause disease, but can lead to infections through breaks in the skin, such as cuts, wounds, or surgical incisions.

A small number (0.5%-2%) of these bacteria have acquired a gene (mecA) that codes for a protein making the bacteria resistant to many antibiotics. These bacteria likely have developed resistance because of increased antibiotic use. The infections are no more severe than regular Staph infections, but are much harder to eliminate due to their antibiotic-resistance.

There are two types of MRSA infections in people based on where they are acquired: health-care associated (HC-MRSA) or community-associated (CA-MRSA). HC-MRSA infections are usually more serious and can involve the bloodstream and/or internal organs. Fortunately, these infections are on the decline due to better infection-control practices. CA-MRSA infections are found mostly in sports settings, child care facilities, or crowded living situations. The bacteria are acquired during personal contact or through shared items such as towels and equipment.

Many people wonder … can my pet give me MRSA? Surprisingly, you are more likely to give the infection to your pet than the other way around. MRSA infections occur infrequently in pets, with the infections being less virulent than in people and usually more easily resolved.

The greater concern for our pets is Staphylococcus pseudointermedius. This bacterium is found on most, if not all healthy dogs and less commonly on cats. Transmission is usually through close contact with other pets. The emerging threat is blamed on improperly used antibiotics and failure to practice good infection control. The incidence of resistant strains in these bacteria (referred to as MRSP) varies widely, but it has been reported in up to 30 percent of dogs. Many dogs harbor these bacteria without illness, but MRSP infections are on the rise.

MRSP infections look like “regular” skin infections, but do not resolve with appropriate empiric antibiotic therapy. When this occurs, testing should include culture and sensitivity to identify the resistant bacteria and help identify an appropriate antibiotic for treatment.

Because it may be difficult to find effective systemic antibiotics, veterinarians should consider topical antimicrobial therapy for superficial infections (flushing wounds, shampoos, conditioners, sprays, ointments, and even the application of honey have all been found to be helpful). It is also important to diagnose and treat secondary invaders (e.g., yeast and non-resistant bacteria) that can complicate infections.

Good hygiene is paramount in preventing infections — resistant or otherwise. Gloves and other protective devices should be worn during contact with affected individuals, followed by proper hand-washing. Infections and wounds should be kept covered, potentially-contaminated items disinfected (e.g., bowls, bedding, and collars), and contact between affected and unaffected people/animals should be prevented.

There is some concern that these infections can be transferred between people and animals, but the true zoonotic potential is not known. Precautions are necessary to reduce this risk in veterinary clinics and in the home.

This post was written by Dr. Jennifer Ratigan, a veterinarian in Waynesboro, VA. I’ve known Jen since before we attended veterinary school together and thought you might like to get her take on the world of veterinary medicine. She’ll be contributing posts to Fully Vetted from time to time.

Dr. Jennifer Coates

References

Weese, J. S. (2012 May) Management of methicillin-resistant Staphylococcal infections. Paper presented at American College of Veterinary Internal Medicine, New Orleans, Louisiana. Accessed on the Veterinary Information Network 11/20/13.

Centers for Disease Control and Prevention. Methicillin-resistant Staphylococcus aureus (MRSA) infections. Accessed October 15, 2013.

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