June 22, 2009 -- The nasty, drug-resistant bacteria known as MRSA may have a new carrier: the family pet. The scourge of hospital wards and locker rooms, MRSA often begins with small red bumps that can turn into painful abscesses requiring surgery to drain them.
If not detected and treated, they can find their way into the body, causing infections in heart valves, lungs, joints, bones and the bloodstream.
Yes, Kitty and Spot may be boon companions, but their friendship comes with the possibility of the transmission of methicillin-resistant Staphylococcus aureus and at least 30 other pathogens, according to Dr. Richard Oehler and his colleagues at the University of South Florida College of Medicine in Tampa.
Many of these bugs are transmitted by bites and scratches, but others -- such as MRSA -- can cycle back and forth between pets and owners, Oehler and his colleagues warned in a review article, which appears in the July edition of the journal Lancet Infectious Diseases.
"Pet owners are often unaware of the potential for transmission of life-threatening pathogens from their canine and feline companions," the researchers said.
Particularly worrisome is a growing body of evidence that cats and dogs can be colonized by MRSA -- germs that are probably acquired from their owners, since cats and dogs usually carry a different strain of Staphylococcus bacteria.
But the cats and dogs can give the bug back. As long ago as 1988, researchers reported that a cat living in a United Kingdom geriatric unit had passed MRSA back to people. Screening of patients and staff showed that 38 percent of the nursing staff there had colonies of the bacteria living somewhere on them.
And that's not uncommon, according to Lawrence McGill, a veterinarian at the ARUP Animal Reference Pathology Laboratory in Salt Lake City, Utah.
"There is more and more data pointing to the [fact that the] most common source for animal infections with MRSA is from humans, including contact with medical facilities where humans are treated," McGill said.
In 2006, researchers isolated MRSA from the skin sores of a three-year-old domestic short-haired cat and -- for the first time in a household pet -- confirmed the pathogen as belonging to the infamous strain known as USA300.
The USA300 clone is a major source of skin infection in community-acquired MRSA in the United States -- and the owner of the cat had indeed experienced repeated soft-tissue staphylococcal infections.
Dogs, Cats May Harbor Germs, But Non-Bite Spread Remains Rare
The treatment of infections from pets is the same as for MRSA acquired from other sources, Oehler said. Mild-to-moderate infections can be treated with oral anti-staphylococcal agents, while more serious disease can be treated with drugs injected into the sites of infection.
But MRSA is not the only potential bacterial threat that pets can harbor. All told, at least 30 pathogens can be transmitted from pets to people, Oehler and his colleagues said, including species of Pasteurella, Streptococcus, Fusobacterium and Capnocytophaga.
Many are transmitted by bites and scratches, the researchers said, noting that in 2001, more than 350,000 Americans were treated in emergency departments for non-fatal dog-bite-related injuries.
In the U.S., dog and cat bites make up about 1 percent of emergency room visits every year, and the numbers are similar in Europe.
Roughly 60 percent of animal bites are by dogs; the cost to treat them exceeds $1 billion per year. Between 10 and 20 percent of animal bites are attributed to cats.
Severe infections can occur in about 20 percent of all dog and cat bites, the researchers said.
When bitten, hands are the most parts of the body to develop infections, as well as to develop rapidly spreading and disabling damage. In fact, between 30 and 40 percent of these hand bites become infected.
But pet lovers need not worry about handling their pets, as spreading the germ in this way is relatively rare.
"Petting or handling pets will not result in infection very easily," McGill said, adding that keeping pets clean, maintaining immunizations and controlling parasites "will go a long ways to keeping the pet and owner healthy."
This article was developed in collaboration with ABC News.