People Can Infect Pets, Study Shows

Scientists who worry about the spread of nasty germs from animals to people have found the opposite can also happen: Cats and dogs catch bad things from their owners.

Canadian researchers documented 16 cases of dangerous, hard-to-treat staph infections in horses, cats and dogs. They believe all of them probably began with owners or veterinarians infecting the animals.

The germ is methicillin-resistant Staphylococcus aureus, or MRSA, a microbe that until recently was seen only in hospitals, where it often spreads to elderly or especially ill people who have open wounds or tubes. Healthy people may carry it on their skin without getting sick.

“We’ve got some pretty strong evidence that owners were responsible for their companion animals developing MRSA soft tissue infections,” said Dr. Donald E. Low, chief microbiologist at Mount Sinai Hospital in Toronto.

Low and colleagues presented the data Sunday at a meeting in Chicago of the American Society for Microbiology.

They found that the animals had resistant staph infections that were genetically similar to the ones that occur in people. In some cases, they showed that the animals got sick months after their owners caught identical germs.

Such transmission is often difficult to prove, but Dr. Shelley Rankin, a microbiologist at the University of Pennsylvania, believes vets are seeing it more often in domestic animals.

“People think it only goes one way, from animals to humans,” she said. “This shows the other side of the story.”

The germ passes through close person-to-person, or person-to-pet, contact, which is one reason why hospitals constantly urge doctors and nurses to wash their hands. In people, staph can cause pimples and boils as well as much more serious conditions, such as pneumonia and lethal bloodstream infections.

The first Canadian case researchers examined was a 9-year-old bichon frise operated on in January 2000 to remove an eyelid cyst. Despite antibiotics, the dog developed a lingering infection that turned out to be MRSA.

The dog’s owner had undergone surgery in late 1999 for testicular cancer. While in the hospital, he too had caught MRSA. The researchers did genetic tests to compare the germs from man and dog. They were identical.

The researchers believe veterinary clinics can also serve as a source of the bug, just as hospitals spread the germ to sick people. Two cats and one dog with identical infections had all been treated at the same Quebec clinic.