Scientists have long known that tiny, insectlike creatures known as dust mites can thrive in homes that look spotless, infesting carpets and furniture and causing allergies to flare.
Now research indicates these bugs may be even more treacherous than had been thought, inciting asthma among children who are exposed to the dust mites at an early age.
The findings do not bode well for children in Seattle, where mild year-round temperatures and humidity offer dust mites one of the nation's prime breeding grounds.
``This is the first time we have scientific evidence that early exposure to high levels of foreign proteins, the dust mite being prominent, greatly increases the risk of asthma,'' said Dr. Thomas A.E. Platts-Mills, a co-author of the study published recently in the New England Journal of Medicine.
The study reinforces the growing belief that asthma can be triggered by a whole host of foreign proteins, from those carried by cockroaches to that found in the saliva of cats and dogs. In the case of dust mites, most people react to the feces they leave behind. One mite drops about 20 such particles a day.
The researchers based their conclusions on a survey of 67 children in the damp south-coastal city of Poole, England, where they found that all but one of 17 one-year-olds who developed asthma by the age of 11 had lived in homes with a high concentration of dust mites.
The study concluded that ``exposing young children to high levels of foreign proteins in their homes should be regarded as an important health risk.''
William E. Pierson, a senior staff member at the Northwest Asthma & Allergy Center in Seattle, said the survey's findings were particularly pressing because Seattle's climate and geography mirrors that of the study.
``Dust mites are a significant problem in the Puget Sound area,'' he said. ``The scary thing is that the rate of childhood asthma has doubled in the last decade, and we're not sure why.''
Platts-Mills pointed to changes in housing construction over the last 30 years as a possible culprit. He said many homes have been so tightly built and insulated that it has caused temperatures and humidity to rise, creating a warm and damp environment in which the microscopic bugs flourish. Fitted carpeting and central heating make it even cozier.
Platts-Mills said the study should signal a shift in the way patients who suffer from allergies should be treated. ``The real question raised by this paper is that up to now most of us waited until allergic patients walked into the doctor's office. Now it's clear we should be thinking about housing design and management,'' he said.
Dust mites like to live in carpets, bedding and upholstered furniture. They grow in temperatures of more than 75 degrees with humidity of more than 55 percent. In a home with polished floors and wooden furniture they have little place to nestle, mature and leave the droppings responsible for the allergic reaction.
To keep humidity levels low in any home, Platts-Mills suggested opening windows and using dehumidifiers and air conditioners. Pillows, sheets, blankets and mattress pads should be washed in hot water every 10 days or so; cold water won't kill the mites.
Pierson said mattresses, box springs and pillows should be encased in zippered, dust-proof covers to inhibit the insects from traveling about.
Because dust mites live deep in a carpet, most vacuuming is ineffective in capturing the insects unless an anti-allergen spray is used. When vacuuming, children should not be present and adults should wear masks because the mites and their droppings become airborne. Shampooing aggravates the problem by enhancing the humidity in the carpet.
In Seattle, the dust mites are more common in the fall, winter and early spring, Pierson said.
A number of new products that act against the mites have recently made it onto store shelves, Pierson said. They include the Acarex Test, a kit that allows you to test for the insect from dust in your vacuum cleaner bag, and Acarosan, a solution sprinkled onto the carpet that congeals around the dust mites, enabling you to vacuum them up in clumps. The products can be ordered through pharmacies.
The battle against these microscopic creatures can be challenging. Without persistence, it can be difficult to break the reproductive cycle. Female mites can lay 25 to 50 eggs that take only three weeks to mature.
For getting started in the anti-mite crusade, Pierson offered a strategy he has found effective in his practice: ``Show a patient a picture of a dust mite. It really motivates them.''