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Mice at the Tail End of Your Asthma Woes

Mice Allergens Are Factors in Asthma in Urban and Non-Urban Homes Alike, Study Shows
WebMD Health News
Reviewed by Louise Chang, MD

March 17, 2008 (Philadelphia) -- Your old house could be at the root of unexplained allergy and asthma symptoms, new research suggests.

A nationwide study shows that mouse allergens in U.S. homes -- once thought only to be an inner-city problem -- are surprisingly common outside urban areas.

Of more than 800 homes surveyed, 82% had detectable levels of mouse allergen. More than one in three homes had levels high enough to increase the risk that occupants would develop allergies.

And in people who already had allergies, elevated levels nearly doubled the odds of having difficulty breathing, persistent wheezing, and other asthma symptoms.

Elevated levels were most commonly found in high-rise apartments, mobile homes, older homes, and low-income households.

Mouse Allergens: Risk Factors for Asthma

Exposure to mouse allergens is a well recognized risk factor for asthma in the inner city, says William Busse, MD, head of the allergy section at the University of Wisconsin in Madison and a former president of the American Academy of Allergy, Asthma & Immunology (AAAAI).

But it's been overlooked as a risk factor outside of those settings, he tells WebMD. Busse moderated a news conference to discuss the findings here at the AAAAI's annual meeting.

The new findings grew out of the National Survey of Lead and Allergens, the first study to estimate indoor allergens in a nationally representative sample of U.S. households.

For this analysis, Paivi Salo, PhD, of the National Institute of Environmental Health Sciences, and colleagues asked nearly 2,500 people living in 831 households in 75 cities and towns nationwide about themselves, their families, their living conditions, and their health, including whether they suffered from allergies or asthma.

Dust samples were tested for mouse allergens from beds, sofas, and chairs, and the floors of bedrooms, living rooms, and kitchens. Field teams inspected each home for mice, cats, and other animals.

Kitchen Floors: High Concentration of Mouse Allergens

Kitchen floors had the highest mouse allergen concentrations of all the places tested, Salo says.

Other mouse-allergen magnets included the bed and bedroom floor, the study showed. Living room sofas and chairs had the lowest levels.

Don't think you're home free just because you don't see mice in your house, Salo tells WebMD. 

That's because mouse urine is the biggest source of the allergens, she explains. "So even if you don't see mice, there are often mice allergens left behind as the urine dries on dust particles."

So how do you know if there's a problem? In general, homes with lots of cracks and crevices are the biggest offenders, she says.

Also, the older the house, the greater the likelihood that it harbors the allergens, Palo says.

Doctors don't routinely test for mouse allergens, she adds. So if you have unexplained symptoms of asthma, you may want to ask your doctor for a mouse skin prick test.

The solution, of course, is to rid your home of mice, but that may not be as simple as getting a cat.  The researchers found no evidence that cat owners had lower levels of mouse allergen in their homes.

But Salo notes that other research has shown that getting a cat could help nip the problem in the bud. And it certainly won't hurt -- unless of course you're allergic to the cat.

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