My dog has MRSA: what does it mean and how to fight the bug (Proceedings)

Canine pyoderma is a common secondary problem, a leading cause of antibiotic use in dogs, and an often frustrating problem for vets and pet owners alike. Unlike many other types of infections, skin infections are often recurrent. This frequently leads to an ongoing cycle of being on and off of antibiotics. The net result is some dogs get treated very regularly and for long periods of time with antibiotics, and it's not particularly surprising that highly drug-resistant bacteria like methicillin-resistant Staph. pseudintermedius (MRSP) eventually become involved.

Most of the time pyoderma develops in response to some underlying skin disease, such as flea allergy dermatitis, food allergy, atopy, Cushing's disease or hypothyroidism. Identifying and treating a skin infection is one thing. Identifying and treating the reason for the infection is another, and that is arguably the most critical component. Ignoring the underlying cause may not be the end of the world for a single infection, because proper treatment and a susceptible bacterium can result in a successful outcome, but ultimately ignoring the real problem can lead to a difficult-to-treat, resistant infection. Any diagnosis of pyoderma should be accompanied by consideration of the underlying cause.

In dogs the main pathogenic methicillin-resistant staphylococcus is MRSP. MRSP is known to colonize people transiently when shed in large quantities by dogs with pyoderma. After the disease resolves carriage also resolves. Nevertheless, infection with MRSP in people, although not common, has been documented. Relative prevalence of MRSP in humans may be unclear due to morphological similarities between MRSP and MRSA. MRSP is becoming increasingly multi-drug resistant in Europe and the United States. In addition to betalactams, it is frequently resistant to gentamicin, tetracycline, macrolides and lincosamides, and trimethoprim/sulfa.

MRSP may be isolated from healthy individuals with no signs of disease; this is considered "carriage" or "colonization", and is distinguished from "infection", wherein the MRSP is causing signs of disease. As multidrug-resistant bacteria such as MRSP become more common in pets, there are increasing questions about how to manage animals that carry them. Limiting the contact with other animals to reduce the spread of the bacterium certainly appears to make sense. However, we also have to realize that this is now a rather common bacterium, and it doesn't cause infections in the majority of animals that get exposed, and it is very rarely a problem in people. That doesn't mean we should ignore it. Sick and immune-suppressed individuals may be at risk to develop an infection with MRSP, especially in high-risk situations, such as hospitals.

Because MRSP infections are becoming so common and people are aware of potential concerns regarding transmission of MRSA from pets to people, it's not a surprise that veterinarians are confronted with that concern by pet owners.

The risks are very low, but they are not zero. While the odds of a client or veterinarian picking up MRSP from a dog are very low, avoiding an infection with a highly drug-resistant bacterium should still be the goal. Accordingly, the use of proper hygiene and infection control measures, particularly around an animal with an active infection, is always important. These measures include:

     • Frequent hand washing after contact with the pet.

     • Avoiding contact with the infected site.

     • Keeping the infected site covered with an impermeable dressing, whenever possible.

     • Reducing contact with the nose of the infected animal, since it may also be carrying the bacterium there. In general, reducing close contact (e.g. snuggling, nuzzling, hugging, and kissing) during the period of infection is a good idea.

     • Regular washing (in hot water with hot air drying, whenever possible) of pet beds and other items that come into close and frequent contact with the pet.

Is all that overkill? Probably, but it's also an easy and practical plan, and a reasonable approach to reduce the already-low risks

Treatment alternatives in dogs with multi-resistant MRSP:

Once MRSP is confirmed by a culture and sensitivity, it is important to address the infection with aggressive systemic and topical therapy. The selection of an appropriate oral antibiotic is based on the sensitivity panel. It is not unusual that MRSP are multi-resistant and occasionally no antibiotic seem to work. Although new antibiotics are available there is a serious concern that abuse of these novel antibiotics may as well become ineffective. It is very likely that we as veterinarians will need to change our strategy of using oral antibiotics to alternative treatment options. Recently several suggestions have been proposed to be used in conjunction, combination, or in rare cases as a sole therapy:

     • Daily baths with a 4% chlorhexidine shampoo

     • Daily topical Chlorhexidine micro emulsion spray and twice weekly bathing the Chlorhexidine PS shampoo

     • Daily Benzoyl Peroxide - Sulfur Sal product followed by TrizChlor4 shampoo (4% chlorhex with trizEDTA) followed by Zymox leave on rinse (without dilution)

     • Daily soaks in diluted bleach 1/2 cup/40 gallons of water

     • Spray Vetericyn VF 2-3x per day (http://www.vetericyn.com)

     • Staphage Lysate (SPL)® from Delmont

     • Allerderm Spot-on weekly

     • Bactroban (mupirocin) and Fuciderm (fucidic acid) ointment daily