For many years, MRSA (methicillin-resistant Staphylococcus aureus) was thought to happen only in humans, until a report of a MRSA infection in a dairy cow was reported in 1972. It has now become an increasingly urgent problem in veterinary medicine, with MRSA infections reported in horses, dogs, cats, pet birds, cattle and pigs.
Q: How are animals involved in the spread of MRSA?
A: If MRSA is present, it is commonly carried on the skin or in the nasal passages of healthy people and/or pets. If an infection is present, it can be found almost anywhere-especially where there's a skin wound or sore. As with human patients, an animal that carries the bacteria on their body but does not exhibit symptoms of disease is considered to be "colonized". Those who do exhibit symptoms are considered "infected".
It was first thought that the transmission of MRSA to animals was only from human to animal, with contact between the hands of the human and nostrils of the animal. There is now increasing evidence that MRSA can be transmitted in both directions, from human to animal (reverse zoonotic) and from animal to human (zoonotic). Once exposed to MRSA, animals can become colonized, and may serve as reservoirs to transmit the infection to other animals and also back to their human handlers (reinfection).
There is a possibility that until the MRSA has been cleared from the animal (and the animal is therefore "decolonized"), re-transmission from animal to human and further human-to-human transmission can occur. A 2008 report in the New England Journal of Medicine documented the same MRSA strain in a chronically infected patient, her family members, and one of three pet cats. Following treatment of the pet cat, the patient's MRSA infection resolved. Similarly, a 2005 case report in the Journal of Clinical Microbiology documented colonization of family members and a pet dog during the investigation of chronic, recurrent MRSA infections in a human patient. The authors concluded that either a family member or the pet dog served as a reservoir for reinfection of the patient.
Q: How common is MRSA in animals?
A: The prevalence of MRSA in the animal population is currently unknown.
Q: Are certain animals at higher risk for acquiring an MRSA skin infection?
A: Yes. As with people, animals with weakened immune systems are more likely to become colonized or infected with MRSA. The risk factors for animals vary with different animal species
Q: What are the symptoms of MRSA infection in animals?
A: While the major threat of MRSA for animals and their handlers appears to be transmission to humans and other animals, animals can become infected. The most common animal infections occur at surgery sites or skin wound sites, but infections can occur that range from skin infections to pneumonia.
Q: I have a patient with suspected or confirmed MRSA. Are there animal-related questions I should ask them?
A: When presented with a patient with suspected or confirmed MRSA infection or colonization, it is critical that you inquire about the patient's contact with animals; this includes pets, visiting animals, resident animals in assisted-living communities, nursing homes, etc. This information is even more important if the patient is immunocompromised or is experiencing chronic, recurrent infections. Although animals are often colonized and not infected, ask your patient if their animal has any signs of skin infection.
Keep in mind that your patient's occupation can also be very important when investigating the cause of MRSA infection. Veterinary personnel and others whose professions involve contact with animals may be at higher risk of MRSA infection and/or re-infection.
Q: There have been questions about possible MRSA transmission between therapeutic animals (eg, animals that visit patients in nursing homes and health-care facilities for psychological benefit). What precautions should be taken when dealing with therapeutic animals?
A: Due to the prevalence of MRSA in health-care environments, therapeutic animals involved in animal-assisted intervention programs (AAIs) may be at risk for MRSA infection or colonization. Lefebvre et al developed a consensus document that put forth standard, evidence-based guidelines for handling AAIs in healthcare settings. These guidelines are mainly directed at health-care facility staff members and the handlers of the therapeutic animals.
In the case of MRSA and therapeutic animals:
Source: Lefebvre SL, Golab GC, Christensen E, et al. Guidelines for animal-assisted interventions in healthcare facilities. Am J Infect Control 2008; 36:78-85.
Q: If my MRSA patient has told me they have a pet, what should I do?
A: Please instruct your patient to take their animal to their veterinarian for an examination and diagnostic testing. Often, a nasal/pharyngeal swab is sufficient. If the animal tests positive for MRSA, the veterinarian will determine the proper course of treatment for the animal.
Q: What is the treatment for MRSA in animals?
A: When animals are found to be colonized with MRSA (usually by testing swabs taken of the nostrils), there is currently no recognized method for decolonizing them. Based on clinical cases observed, many experts believe that companion animals are generally transient carriers of MRSA, which means they are colonized for about 2-3 weeks; antibiotic treatment to decolonize the animal may not be necessary. Isolating the animal from the human until the animal is no longer colonized is likely to be effective in preventing reinfection of the human.
In cases of skin infections - the most common type of infection found in animals - some options may be either applying antibiotic cream to the skin infection, or treat the animal with other antibiotics, or a combination of both. Your veterinarian will determine the appropriate treatment for your animal based on their exam, the animal's history, and the laboratory results.
Q: Can I or my patients get MRSA by eating meat or dairy products from an infected/colonized animal?
A: MRSA outbreaks have occurred from food through contamination by infected food handlers, but this is very uncommon, and this risk can be prevented by proper pasteurization and food handling. To date, there have been no confirmed cases of food-borne MRSA infection from animals.
This information has been prepared as a service by the American Veterinary Medical Association. Redistribution is acceptable, but the document's original content and format must be maintained, and its source must be prominently identified. Please contact Dr. Kimberly May (800.248.2862, ext 6667) with questions or comments.