Staph infections and Methicillin Resistance in Companion Animals

Staphylococcus (staph) bacteria are all around us in an intimate way since it normally lives on the skin and mucous membranes of both people and animals alike. It usually is not of a concern to the individual if the skin is functioning normally and there is not a risk for infection (e.g., systemic illness and immune compromise). When infection is present, usually of the skin, most staph bacteria are susceptible to commonly prescribed antibiotics. Although many individuals walk around every day with staph bacteria, not all staph are alike. Indeed, Staphylococcus aureus prefers people (as well as pigs and some horses) over dogs and cats, Staphylococcus pseudintermedius likes the skin of companion animals over man.

"Methicillin-resistant staph" refers to Staphylococcus bacteria that have developed a resistance to commonly prescribed penicillin and penicillin-like antibiotics, making infections difficult to treat. Again, most staph bacteria are susceptible to a wide array of antibiotics, but these particular staph have developed resistance to typical antibiotics, hence they are more challenging to eliminate.

Dr. Adam Patterson, clinical assistant professor and chief of dermatology at the Texas A&M College of Veterinary Medicine & Biomedical Sciences Small Animal Hospital, explained staph skin infections (pyoderma) in animals present as skin sores recognized as redness, pimples, scabs, dander, and hair loss. Many times these infections itch and result from uncontrolled allergic skin disease. When this type of infection occurs, it usually responds to correctly prescribed and administered topical and/or systemic antibacterial treatments.

If the infection is not easily treated by an appropriate course of antibiotics, then the chance for a "resistant" infection is heightened. Although subject to debate, as this is an area of ongoing research, Patterson said risk factors for methicillin-resistant staph infections in both people and animals seem to include repeated courses of antibiotics, chronic skin disease, immune compromise, recurring hospital visits, and indwelling medical implants such as those used for orthopedic surgery. When these risk factors are present in animals with pyoderma, veterinarians perform a culture of the skin sore to determine if the bacteria are indeed methicillin-resistant.

"A resistant infection doesn't look different than susceptible infections, the only way to know is to culture the skin," Patterson said.

Once it is confirmed the pet is infected with methicillin-resistant staph, the veterinarian can determine the best course of action. Patterson said the most common treatments are topical such as antiseptic shampoos and culture-based systemic antibiotics.

"When we can, we try to treat them topically," Patterson said. "Methicillin resistance doesn't mean that the bacteria are more pathogenic, they just are not killed by common antibiotics anymore."

People with methicillin-resistant staph are said to have MRSA (methicillin-resistant Staphylococcus Aureus). Since dogs and cats tend to have a different species of staph on their skin, resistant bacteria are most often called methicillin-Resistant Staphylococcus Pseudintermedius (MRSPi or MRSP). People are normally not infected with MRSPi; likewise, dogs and cats are normally not infected with MRSA. Common transfer of MRSPi from pets to people has been fairly rare and isolated to date, while transfer of MRSA from people to pets is somewhat more likely. Again, MRSPi is predominantly found in companion pets, while MRSA is primarily found in people.

"We don't know much about dog-to-dog spread, but it is a large component of research on the epidemiology of methicillin resistance as we move forward," Patterson said.

A few simple recommendations to help reduce the chance of transfer of staph bacteria between household people and pets once an animal has confirmed MRSPi infection include: administering the veterinary-prescribed treatment as directed, wearing gloves when treating the affected pet with topical therapy, keeping young children and immuno-compromised people (cancer, HIV/AIDS, etc.) away from the affected pet, keeping personal skin wounds covered and protected, discouraging the pet from licking the face of people, and not letting the affected pet share the bed or linens with household persons. Above all, Patterson emphasized the need to wash all surfaces of the hands after handling the affected pet.  Additionally, a search into why the pet has a resistant infection should be undertaken and corrected once identified.

If you develop skin sores or have concerns about your personal health once a methicillin-resistant staph infection has been confirmed in your pet, then consult your physician.

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