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Photo Credit: Susannah Kay

Methicillin Resistant Infections

Nancy Kay, DVM  speakingforspot.com

For several years now there has been a good deal of press about methicillin resistant Staphylococcal infections in people. Such infections are now all too common in veterinary patients as well. Staphylococcal bacteria are normal residents on the skin surface in humans and animals. Although they are part of the body’s standard flora, they are “opportunistic” little buggers, meaning they will gladly create infection when a good opportunity arises such as an inflammatory condition, a wound, a surgical incision, or a compromised immune system.

In humans, methicillin resistant infections typically involve Staphyloccocus aureus, therefore the designation MRSA. While animals occasionally develop MRSA, they are far more commonly infected with methicillin resistant Staphylococcus pseudointermedius, therefore the designation of MRSP. What MRSA and MRSP share in common is a particular gene that confers antibiotic resistance against methicillin and a variety of other antibiotics including penicillins and cephalosporins.

MRSP infections in dogs and cats

MRSP infections in dogs and cats most commonly affect the skin, ears, and urinary bladder. Symptoms of methicillin-resistant infections are identical to those that are methicillin-sensitive. Evidence of a skin infection varies from small raised red bumps to open oozing sores. The feet are commonly affected. Symptoms of ear infections often include redness, tenderness, and discharge within the ear canal. Bladder infection symptoms may include straining to urinate, increased frequency of urination, inappropriate urination (the well house trained dog is now soiling in the house), and blood within the urine. Veterinarians suspect methicillin resistance if the symptoms fail to improve or worsen in response to conventional antibiotic therapy. Methicillin resistance is confirmed with a culture that identifies the species of bacteria along with its susceptibility to a variety of antibiotics. 

Treatment of MRSP

Treatment of methicillin resistant skin or bladder infections in dogs and cats requires oral antibiotics. The drug choice should be based on bacterial culture and antibiotic susceptibility testing. The antibiotics most commonly used are sulphonamides, chloramphenicol, clindamycin, rifampicin, doxycycline, and minocycline. Sulphonamides can cause diminished tear production (dry eye). For this reason, measurement of the animal’s tear production should be measured before and during treatment with these antibiotics. Chloramphenicol can result in bone marrow suppression in people so special precautions should be taken when handling this medication. Vancomycin and linezolid are typically very effective against methicillin resistant infections, however it is recommended that these drugs be reserved for human MRSA patients with hopes of preventing development of antibiotic resistance from overuse. The duration of treatment with oral antibiotics depends on the severity of the infection, but a minimum of three weeks is typically recommended.

Topical therapy (treatment applied directly to the site) is very important in conjunction with oral antibiotics when treating skin or ear MRSP infections. For milder ear infections topical therapy may be all that is needed. Medicated shampoos and frequent bathing may be prescribed. Clipping the hair away from infected skin sites may be necessary for best results.

Recommended precautions

If your dog or cat has an MRSP infection, what precautions should be taken to avoid developing the infection yourself? The good news is that reports of infections in humans exposed to MRSP are exceedingly rare. Veterinarians who specialize in dermatology experience daily exposure in the workplace (MRSP skin and ear infections are so darned common), yet there have been no reports of infection amongst these specialists.

If your dog or cat has an MRSP infection, pay attention to good hygiene. The most important precaution is frequent and thorough hand washing with soap and water after touching or handling your pet and his or her food bowls and bedding. Regularly wash collars, leashes, toys, pet bowls, and bedding. Wash pet bedding, towels, and pet clothing separately from the rest of the household laundry, and dry on high heat. And, perhaps the most difficult step- your pet should not sleep on your bed until the infection is fully resolved. Special precautions should be taken with children (they are not the most diligent hand washer). Lastly, anyone who is pregnant or at increased risk for infection (HIV positive, taking medications that suppress the immune system) should take preventive measures based on advice received from their own physicians.

What about other dogs and cats in the household? They do not need to be separated from the pet with the active infection unless they have immune system compromise, an open wound, or some other factor that predisposes them to infection. Dogs with active MRSP infections should ideally be kept away from community venues (dog parks, doggie day care, training classes, pet facilitated therapy) in order to prevent exposure to individuals who may be more susceptible to infection.

A final note

It is thought that the increased prevalence of methicillin resistant Staphylococcal infections is caused, at least in part, by the overuse of antibiotics. I can certainly attest to the fact that, within the veterinary profession, antibiotics are often prescribed without good reason. If your veterinarian recommends antibiotic therapy for your pet, I encourage you to request justification for doing so. Ask for a description of the indicators that suggest a bacterial infection is the cause of your pet’s symptoms. The very best evidence is a culture that documents the presence of infection. Treatment based on culture, rather than simple suspicion, is the ideal standard of care.

Have you ever had to deal with a methicillin resistant infection?  Comments at speakingforspot.com.

Best wishes,

Nancy Kay, DVM

Diplomate, American College of Veterinary Internal Medicine
Author of Speaking for Spot: Be the Advocate Your Dog Needs to Live a Happy, Healthy, Longer Life
Author of Your Dog’s Best Health: A Dozen Reasonable Things to Expect From Your Vet
Recipient, Leo K. Bustad Companion Animal Veterinarian of the Year Award
Recipient, American Animal Hospital Association Animal Welfare and Humane Ethics Award
Recipient, Dog Writers Association of America Award for Best Blog
Recipient, Eukanuba Canine Health Award
Recipient, AKC Club Publication Excellence Award
Become a Fan of Speaking for Spot on Facebook

Please visit http://www.speakingforspot.com to read excerpts from Speaking for Spot and Your Dog’s Best Health.   There you will also find “Advocacy Aids”- helpful health forms you can download and use for your own dog, and a collection of published articles on advocating for your pet’s health. Speaking for Spot and Your Dog’s Best Health are available at www.speakingforspot.com, Amazon.com, local bookstores, and your favorite online book seller.

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