Tie to Pets Has Germs Jumping to and Fro
Tie to Pets Has Germ Jumping to and Fro
But in recent years, the germ has become a growing problem for veterinarians, with an increasing number of infections turning up in birds, cats, dogs, horses, pigs, rabbits and rodents. And that, infectious-disease experts say, is becoming a hazard to humans who own or spend time with these animals.
“What’s happened for the first time that we’ve noticed is that you’re getting flip back and forth,” said Scott Shaw, head of the infection control committee at the Cummings School of Veterinary Medicine at Tufts University.
It is unknown how often pets play a role in human infections by methicillin-resistant Staphylococcus aureus and vice versa; physicians and veterinarians do not routinely trace such infections to their source. When such scientific sleuthing is conducted, however — usually in the case of multiple or recurring infections — the results suggest a strong link.
In 2008, for example, an elephant calf and 20 of its caretakers at the San Diego Zoo contracted MRSA skin infections. An investigation by the zoo and state health officials determined that the calf, which was eventually euthanized, had probably been infected by a keeper who unknowingly carried the bacteria. (The case was reported in The Morbidity and Mortality Weekly Report.)
Still, experts are not recommending routine testing of pets and their humans. Instead, they call for the same kinds of precautions that apply to other pathogens, especially frequent washing or sanitizing of hands before and after playing with a pet.
The first cases of MRSA in pets, about five years ago, appeared to be in therapy dogs and other animals exposed to patients or health care workers. Those animals are still thought to be at greatest risk, but the pattern might be changing.
In a study this summer in The American Journal of Infection Control, Elizabeth A. Scott and her colleagues at the Center for Hygiene and Health in Home and Community at Simmons College in Boston swabbed household surfaces like kitchen and bathtub drains, faucet handles, toilets, high chairs, trash cans and kitchen sponges at 35 randomly selected addresses to see what germs they would find. They found MRSA in nearly half of the homes they sampled.
When they tried to figure out what might make it more likely to have the bacteria at home, they ruled out many supposed risk factors, including working out at a gym, having children who attended day care, having a recent infection or recent antibiotic use, and even working in a health care facility.
The one variable that overwhelmingly predicted the presence of the germ was the presence of a cat. Cat owners were eight times more likely than others to have MRSA at home.
“There are a number of papers coming out now showing that pets pick up MRSA from us,” Dr. Scott said, “and that they shed it back into the environment again.”
Dr. Scott’s next study will screen patients scheduled for elective surgeries. When she finds MRSA, she will also test their pets to determine how common that transmission might be.
“This is a burgeoning epidemic,” said Dr. Richard L. Oehler, an infectious disease specialist at the University of South Florida College of Medicine in Tampa, who reviewed case reports of MRSA’s jumping between people and animals. Dr. Oehler’s paper appeared in July in The Lancet.
Dr. Oehler recounted the case of a diabetic man with recurrent MRSA skin infections that were eventually traced to his dog, a Dalmatian who carried the bacteria but was not ill.
“He would sleep with the couple in the bed and lick them in the face,” said Dr. Farrin A. Manian, chief of infectious diseases at St. John’s Mercy Medical Center in St. Louis.
Dr. Manian believes the dog was infected by its owner, but then served as a reservoir for the bacteria, reinfecting his patient.
“Only after we treated all three members of the family were we able to get rid of the infections,” Dr. Manian said.
Then there was the case of the 15-year-old girl and her calico cat; both developed MRSA infections. DNA fingerprinting confirmed that the bacteria in wounds on the girl’s arm and near the cat’s tail were the same.
J. Scott Weese, a veterinary internist and microbiologist at the University of Guelph in Ontario, believes MRSA infections transmitted between people and animals are relatively rare.
His tests of randomly selected dogs, for example, have shown that at any given time only 2 to 3 percent carry MRSA on their fur or skin or in their saliva. And even if a pet becomes colonized, meaning that the bacteria take up residence and reproduce, veterinarians say most healthy animals should be rid of it in a matter of weeks.
For protection, Dr. Oehler recommends hand washing or using hand gels before and after playing with a pet, not letting a pet lick people around the face, and not washing pet food or water bowls in the same sink that food is prepared.
People should also wear gloves when attending to pets that have open wounds, he said, and should keep any of their own broken skin bandaged.
And Dr. Oehler advised owners to be more attentive to their pets’ health in general.
“In many of these cases, there was a lack of awareness that the animal was ill,” he said. “If a pet has a wound, they need that evaluated.”
Dr. Weese, who estimated that relatively few animals were infected, nevertheless agreed that attentiveness was in order. “In the grand scheme of things with MRSA, pets are a pretty minor thing,” he said. “But when you consider how many MRSA infections are occurring in North America at the moment, if they’re a minor component of a major disease, that’s still something we need to be aware of.”
And pets may pose a particular hazard because their relationships with people can be very close.
“If you think about the individuals with whom you have the closest contact in terms of duration, intensity, intimacy, in most people, it’s going to be the spouse, then small children, then pets,” Dr. Weese said. “For some people, pets are No. 1 on the list.”