MRSA in Pets

Methicillin resistant infections in people have been an on-going concern for doctors and hospitals. Estimates show that 30-40% of Staphylococcus aureus (MRSA) organisms cultured from clinical infections are resistant to this antibiotic.

1) MRSA has been termed by the press as a "super-bug". This refers to the resistance this bacteria has against several types of common antibiotics, especially those in the penicillin and cephalosporin families.

2) Other Staphylococcus species have also developed this sort of resistance and are more common in cats and dogs. These include Staphylococcus pseudintermedius (MRSP) and Staphylococcus schleiferi (MRSS).

3) Methicillin is a beta-lactam antibiotic introduced in the 1950s to combat penicillin resistant staph infections. Resistance to methicillin can be acquired from mobile genetic elements containing a gene that stops the antibiotics from binding to the bacteria. These strains are resistant to all penicillins and cephalosporins.

4) MRSA is commonly associated with infections acquired from hospitals (nocosomial infections). MRSA infections have increased hospital stay costs when compared to routine staph infections. Recently, there have been increasing numbers of MRSA infections in people in the community, including people without risk factors traditionally associated with MRSA infections.

5) Estimates show that 0.8% to 3.5% of people in the US have MRSA colonizing their nasal passages. In one large survey evauating S. aureus colonization of households, 1.5% of dogs and 0% of cats carried MRSA and when bacteria were found, they were most often the same strain as the dominant regional nocosomial and community strains.

6) Thankfully, most pets or people exposed to MRSA do not develop any sort of clinical disease. The organism can be cultured from wounds, otitis and pyodermas, but there is not an increase in mortality or morbidity in our pets when compared to methicillin susceptible infections.

7) More commonly, pets are likely to harbour methicillin resistant Staph. Pseudintermedius (MRSP). The prevalence of this pathogen in healthy dogs can be 1.5% to 2% and up to 4% in healthy cats. Up to 7% of dogs with inflammatory skin disease harbour MRSP.

8) MRSP infections are reported in superficial and deep pyoderms, otitis and wound infections. MRSP does not seem to be more virulent than methicillin susceptible strains and treatment for the bacteria can be successful, although the resolution time is usually longer.

9) Methicillin resistant Staph. schleiferi (MRSS) is a relatively new pathogen showing up in dogs. Although this strain is isolated less often than other strains, the incidence of methicillin resistant appears to be higher than the aureus or pseudintermedius strains.

10) The good news in all of this is that, for the time-being, it appears that our pets are temporary carriers of MRSA and that people carrying MRSP were asymptomatic. Evidence showing direction of transmission of these pathogens is circumstantial at this time and more studies are needed.

11) Pet owners can minimize the possibility of transmission between pets and people by simply washing their hands regularly after interactions with their pets. In addition, if you notice any sort of skin infection on your pet, have your veterinarian examine the pet as soon as possible.

12) For up to date and accurate pet health information, visit the Veterinary News Network (www.MyVNN.com) on Facebook.

If you have questions about MRSA and your pet contact Dr. Underwood of Trumann Animal Clinic at catdoc56@pcsii.com