By Christie Long
One of the hottest topics in human medicine in recent times is multidrug resistant skin infections. In people, these infections are caused by the bacteria Staphylococcus aureus, and the term “methicillin-resistant Staphylococcus aureus” or MRSA (often pronounced mer-sa) is used to describe them.
The idea that an infection might be resistant to certain antibiotics is not new, but what is frightening about MRSA infections is how quickly this resistance has emerged. Dogs and cats can get similar skin infections, although the pathogen at work is Staphylococcus pseudintermedius. Consequentially these infections are called MRSP infections. Both bugs have a gene that affords them resistance to all antibiotics in the beta-lactam class, including all generations of penicillins and cephalosporins — two very commonly used types of antibiotics.
Since pets and people seem to be impacted by different types of Staphylococcus infections, people can’t get these infections from their dogs, right? Unfortunately, the answer is somewhat complicated. Based on what we know from several studies of people who work in veterinary hospitals, it’s very difficult for people to get MRSP infections from dogs, but it is possible when owners are caring for pets with deep methicillin-resistant skin infections. People have also been infected by being bitten by dogs.
Pets seem to acquire MRSP infections from healthy, nonaffected pets that carry the bacteria. A pre-existing cut or sore typically affords an entry for the bacteria. The human pathogen, MRSA, has also been found in deep skin infections on pets. In these cases, the likely source of infection is contact with an infected human. Because of this it’s a good idea to keep therapy pets out of hospitals while they have open skin lesions.
When a methicillin-resistant lesion is present, extra vigilence is warranted, such as avoiding direct contact with lesions (wear gloves when applying medications) and frequent and thorough hand washing after touching the pet, its food bowls and bedding. While the infected pet does not need to be quarantined, it’s wise to avoid doggy day care, dog parks, and contact with other pets that have wounds or chronic skin disease. Bowls, toys, bedding, collars and leashes should be washed frequently and separately. Pets with MRSP should not be allowed to sleep with children.
Although it’s scary to think about your pet having such a serious infection, appropriate treatment can be successful. Oral antibiotics are chosen based on a process known as culture and sensitivity. This involves taking a sample of the infected tissue and growing it on a culture plate, identifying the bacteria, and then testing multiple antibiotics against it to determine which one works best to kill the bacteria. Potentiated sulfonamides and chloramphenicol often work, as do clindamycin and minocyline. Vancomycin and linezotlid are typically not used in veterinary medicine, as their use has been reserved for human patients with MRSA infections. Topical therapy including daily bathing with medicated antibacterial cleansers is warranted as well. Treatment continues until the infection is completely resolved and can often take weeks to months.
Christie Long is a veterinarian at the VCA Animal Hospital in Fort Collins, CO. Long left her job in software sales in 2000 to travel for 13 months. Along the way, she was touched by the plight of the animals she saw and somewhere in the Nepalese Himalayas she vowed to return to school to become a veterinarian. While she often finds end-of-life situations heart-wrenching, she considers herself blessed to be called upon as a trusted adviser to families during difficult times. Dr. Long’s family includes her husband and travel partner, Wiley, their 5-year-old son, Wiley IV, their dogs Pancake and Gizmo and cats Sneaky and Sidh.