It is inevitable that you will encounter a methicillin-resistant staphylococcus (MRSA) case in practice. It is also likely that you will have a client with MRSA and be asked about transmission of this type of bacteria to their pet. Because these infections are becoming more common, knowledge of this subject is important to the health of your patients as well as your NAVLE review.

Pyoderma is extremely common in pet patients and is seen almost daily. MRSA infections really appear no different than one of the typical pyoderma skin infections you see. Clinical signs of pyoderma include pustules, alopecia or hair loss, crusts, erythema of the skin, scaling, or ulcerations. If you see a patient that has these symptoms and is NOT responding appropriately to empiric antibiotic therapy, what should you do?

If you have a poor responder, take the following steps:

1 ) Perform a skin cytology – While we all know grossly what pyoderma looks like, take a moment to go forward with a skin cytology to document the presence of bacteria. Sometimes fungal infections may look similar. Don’t forget to do a skin scraping in case the pyoderma is secondary to an underlying cause such as Demodex.

2 ) Before you automatically change antibiotics, perform a CULTURE and sensitivity/specificity right away! This is how MRSA is truly diagnosed and delaying this important diagnostic may be detrimental to the patient.

How do you do a culture like this since there are so many bacteria that may normally and typically be found on the skin? The best way is to use a sterile culture swab and take a sample of fluid inside an intact pustule, wet a sterile swab with sterile saline and rub under some scales, crusts, or around the rim of an epidermal collarette; you can obtain a punch biopsy if the tissue is severe and deep pyoderma is present, or otic exudates if the infection is in the ear.

CULTURE POSTIVE for MRSA: Now what?

If the culture is positive, make sure that the lab includes the sensitivities of chloramphenicol, amikacin, and doxycycline which are not always included. If the culture is positive for Staphylococcus but is not speciated, make sure to request that they report the species. Prognosis for most pets is good with the right therapy. Always treat aggressively with AT LEAST 3 weeks of the appropriate antibiotic (and never penicillin or cephalosporins) and 1 week beyond complete healing. (Coyner, January 2013). Chlorhexidine topically as a cleanser or spray and mupirocin ointment can be good adjunctive treatments for localized infections. Medicated shampoos can be helpful and used every couple of days during therapy.

IS THIS BACTERIA ZOONOTIC?

Yes, MRSA is zoonotic and you should inform the owner as such. However, in order not to create panic, let them know that transmission is still rare and inform them about what they can do to minimize chances of transmission (hand washing, avoiding direct contact especially to open wounds, frequently washing bedding, no licking or kissing on the face, good hygiene, etc.) It is more of a concern in humans that are immunocompromised. That said, veterinarians should never make recommendations for preventing or diagnosing this disease in humans and thus always recommend that they talk to their physician if they are having specific concerns about their own health issues.

As veterinarians, it is important now more than ever that we are conscious about what antibiotics we are prescribing and for what we are prescribing them. It is best to use topical antimicrobials when possible and to rely on oral antibiotics only when truly needed.

Some animals can be “colonized” or carriers of methicillin-resistant staph strains but are not clinically infected. Typically, if a pet is colonized, systemic antibiotic therapy is not recommended. Colonized animals can harbor the bacteria in their nose, mouth, nares, mouth, anus, groin, and head (Griffeth GC, 2008).

PREVENTING THE SPREAD OF MRSA

If you know or suspect a dog has MRSA, keep them isolated from other pet patients. Take them to a room immediately on arrival and don't allow them to sit in the waiting room where there are other patrons. Use gloves and gowns when handling these pets. Hand washing, as always, is one of the most important prevention measures. Properly clean your stethoscope and clothing when exposed and use thermometer covers or dispose of thermometers used on that patient. MRSA can survive for months on fomites/inanimate objects. Just as you would with a parvo case, disinfect the rooms, tables, floors, sinks, light switches, etc. in areas the patient has been.

If you have a severe case you are dealing with and are having difficulty, consult with a board certified dermatologist and infectious disease veterinarian to help you.

References and further reading:

Griffeth GC, Morris DO, Abraham JL, et al. Screening for skin carriage of methicillin-resistant coagulase-positive staphylococci and Staphylococcus schleiferi in dogs with healthy and inflamed skin. Vet Dermatology 2008; 142-149

Coyner, KS. Managing MRSA, MRSP, and MRSS dermatologic infections in pets. Veterinary medicine dvm360 peer-reviewed magazine journal. January 2013, Volume108; 32-38

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