Deadly bacterial infections have been on the rise in recent years as some microbes are gaining resistance to existing antibiotics.

These superbugs, as researchers call them, once were seen as a problem mostly in hospitals, but lately the resistant infections also are cropping up more and more outside hospitals.

Scientists have now begun to suspect that pets could be at least partly to blame. Methicillin-resistant Staphylococcus aureus (MRSA) can be fatal in humans and has proven particularly virulent.

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The superbug can live on the skin or in the nose of a person or pet and not produce symptoms, researchers say. But when it enters a wound, any wound, it can create serious infection that often resists multiple types of antibiotics.

In 1974, MRSA infections accounted for 2 percent of the total number of staphylococcal infections. By 2004, that figure was 63 percent, according to the Centers for Disease Control.

"We used to think of these antibiotic-resistant infections as a healthcare issue that appeared in post-operative or long-term patients," said Stephanie Kottler, a veterinarian at the University of Missouri-Columbia Veterinary Medical Teaching Hospital.

"However, we have been seeing more of these infections that have been acquired throughout the general population, or 'community acquired' infections," she added. "It's important to know what environmental factors might be encouraging or prolonging these infections."

'Multiple cases'

While evidence that points to pets helping to infect humans is so far slim, Kottler and University of Missouri-Columbia colleagues Leah Cohn and John Middleton announced today they will study the issue, which is hinted at in some previous research.

"There are multiple case reports of humans with infection with MRSA when the household pet was also found to have MRSA," Cohn told LiveScience. "Sometimes, the human infection could not be successfully eradicated until the animal was also treated."

Studies have been relatively small and somewhat inconclusive, however.

For instance, a small 2005 British study of a vet facility, detailed in the journal Emerging Infectious Diseases, "suggests that dogs can act as reservoirs of MRSA, which can pose a public health risk to owners and veterinary staff."

A 2003 report in the journal Clinical Infectious Diseases found that two dog owners who suffered persistent MRSA infections relapsed every time they returned home from the hospital. The dog was found to carry the same strain of MSRA, but the researchers could not determine whether the dog initially acquired the infection from the humans or the other way around.

'Seems likely'

Other researchers have shown animals indeed suffer MRSA infections and that the strain, at least in some pets, can be the same as the type that infects humans.

It's also established that veterinarians are more likely to be colonized with MRSA than those uninvolved with health care, Cohn said.

"It seems likely that the bacterium can be transmitted from man to animal, and vice versa," Cohn said, adding: "We do not suspect that dogs and cats are the primary reservoir for infection of people, and there is no reason to think that a healthy pet poses a risk of MRSA infection for a healthy person."

The study

The new study will examine more than 700 pairs of people and their pets. One goal is to determine which strains of MRSA are carried by different types of pets in various settings.

"This study will help us track where the disease started and determine what questions the physician should be asking if a patient is diagnosed with MRSA," said Middleton, an associate professor of food animal internal medicine.

Disease spread from animals to people is not uncommon.

Humans long ago acquired pubic lice, for example, from gorillas, researchers think. AIDS hopped from other primates to humans, and human diseases are also known to kill animals.

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