Veterinary Professionals Infected with MRSA or "Super Bug" Can Pass Disease to Animals

Four hundred and seventeen veterinary professionals were tested for Methicillin-Resistant Staph Bacteria (MRSA), an emerging and sometimes fatal infectious disease that affects dogs, cats, horses, cows and people, during the ACVIM conference June 1-4, 2005, in Baltimore. “We isolated MRSA from a greater percentage of people than we were anticipating,” said Scott Weese, DVM, DVSc, DACVIM, who spearheaded testing. “This is a big deal,” he added. “It’s not just being over-hyped.”

Veterinarians are working with human doctors, and the Centers for Disease Control has been kept apprised of the research, according to Weese, who published an MRSA paper in the May issue of JAAHA and expects to publish another abstract within the next few months.

Despite high incident reports of MRSA infections, locally and abroad, Weese believes that professionals may be seeing a tip of the iceberg because of false negative test results, infrequent testing, and a lack of understanding of the disease. He encouraged veterinary clinics to educate clients about the disease, develop protocols and test animals and staff frequently to prevent the spread of MRSA. “Be proactive instead of reactive,” Weese said.

First identified in the United Kingdom in 1961, MRSA is resistant to multiple drugs, but it is not hypervirulent, Weese emphasized. “It’s just harder to treat, which is why antibiotics should be used sparingly,” he said. Isolation is the best approach to treatment, he added. “You can eliminate MRSA on your own over time if you’re not reinfected.” He advises clinics to take bacterial cultures of specimen and conduct antibiotic susceptibility testing to confirm that the presence of the abnormal penicillin binding protein that is associated with MRSA is present. “For colonization (carriers), we test nasal and rectal swabs,” Weese explained. Test results take between 48 and 96 hours. “The problem is that not all labs identify S. aureus specifically. Some only report coagulase-positive staphylococci, which could be S. aureus or a few other staph, and some labs do not test for methicillin-resistance.”

Healthy animals and people can carry the bug for seven to nine months without showing signs unless they develop secondary infections. For this reason, Weese encourages clinics to test staff members regularly and isolate anyone with MRSA. Doctors are most concerned about transmission to infants, elderly or immunosuppressed people who can develop secondary infections, like pneumonia and septicemia, which can be fatal because of the MRSA component.

Described by consumer newspapers as a “Super Bug,” MRSA started out as a hospital infection and has become a community-associated infection that can be transmitted from human to animal and vice versa, Weese said. He gave examples of such transmission in Washington state, New York and Pennsylvania and urged practitioners to request MRSA tests from their labs. “I think we might be under-reporting in animals,” Weese added. “There are probably a lot more cases of transmission than we know about.”

MRSA can avoid detection despite tests, Weese said. “You can see false negatives with oxacillin testing. It is only expressed when it needs to.” One suggestion that he made was to look for penicillin abnormal binding genes, which can indicate a problem. However, many clinics are not testing for MRSA.

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