by Dr. Dave Erlewein

In the last few years, popular media has put out countless stories about MRSA (pronounced merr-sa) infections, and some of the stories are quite scary. The acronym stands for Methicillin-Resistant Staphylococcus aureus. Staphylococcus aureus is a bacterium presented typically in the nasal passage of about a third of the general human population. While dogs and cats do not commonly harbor this bacterium, they occasionally do so. Most of the time this organism causes no problems, but it is a bug that will take advantage of a human or animal with weakened defense mechanisms or wounds. Both people and animals can carry MRSA without any signs of infection, and this is known as colonization.

When bacteria are cultured from a wound or other areas such as the nose or throat, they are tested against several antibiotics to determine which antibiotics are capable of eliminating the organism. Staph aureus can be either Methicillin-resistant or Methicillin-sensitive. The problem with the Methicillin-resistant staph (MRSA) is that the resistance is not just to Methicillin but to all the penicillin-class antibiotics and most of the other common antibiotics. This makes these infections extremely difficult to treat.

In dogs, the most common MRSA infections tend to be in the skin, wounds and lacerations, and after surgical procedures. MRSA has also been found in ears, the anal area, the urinary tract, and the eye. Risk factors for dogs tend to be similar to those in humans: wounds, surgery, and weakened immune systems resulting from disease and/or medications. Pets used in visitations to hospitals, nursing homes, and hospice houses may be at increased risk for MRSA.

Currently, canine infectious disease experts think that most of the MRSA found in pets originated in humans; however, there have been cases of MRSA that originated in dogs. Pets colonized with MRSA tend to harbor the bacteria in their noses and around the anal area. Contact with MRSA can result in colonization, infection, or both. Hand-washing and use of alcohol-based hand sanitizers is the easiest way to prevent transmission of MRSA from pets to humans.

MRSA infections are diagnosed on the basis of bacterial culture and antibiotic sensitivity testing and results may not be known for 3-5 days. Some newer tests are being developed in humans that will yield results within hours, but these are not available for pets at this time. Currently, we are not sure of the best location at which to check healthy pets for MRSA, but cultures are usually obtained from the nose and anal area.

Most dogs with MRSA colonization tend to eliminate the bacteria on their own within a few weeks. Treatment is usually not needed, but good infection control practices are imperative. This includes frequent hand-washing after handling your pet; not allowing the pet to lick your hands, face, or any area with broken skin; keeping your pet off the beds and furniture; not allowing your pet to have contact with people being treated for cancer, AIDS/HIV, or receiving immunosuppressive drugs. While the importance of the environment in transmission of MRSA is unclear, toys and bedding should be cleaned or changed as frequently as possible to reduce exposure to the bacteria. MRSA-positive dogs should not be exercised in dog parks and areas where there are lots of other dogs and people. As MRSA can be found in the stool of colonized animals, prompt removal of stools is important.

If your pet is diagnosed with MRSA, don’t despair. Most dogs with MRSA can be treated successfully. Follow your veterinarian’s instructions carefully and do not discontinue antibiotics early even if your pet seems cured! Wear gloves when cleaning or treating infected areas and if possible, keep the area bandaged or covered. Promptly dispose of all sponges, gauze, or bandages after cleaning, and change the bandage frequently. Wash you hands after handling your pet and make frequent use of an alcohol-based hand sanitizer. Do not kiss your pet!

If the shoe is on the other foot and you are the one infected with MRSA, there are a few simple precautions you should take to protect your pet. Do not let your pet lick your face or any areas where you have sores or broken skin, and do not kiss your pet. Wash your hands and use a sanitizer before petting or handling your dog and do not touch your face or mouth while handling or petting your dog. When you are done handling your pet, wash your hands again. Wash your hands before feeding your pet or handling food and feeding utensils.

Pets can act as carriers of MRSA, and even though several humans in the household may acquire MRSA, the pet is not necessarily the source. More frequently, the pet is acquiring MRSA from the humans.

Preventing exposure to MRSA in both people and pets is impossible as there are many human and canine carriers of the bacterium. Good hygiene and prompt treatment are the best things that we can do. In addition to humans, dogs, and cats, MRSA has been found in horses, livestock, and wild birds. Currently, however, role of animals in the colonization of MRSA in humans is understudied and undetermined.

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