Mouse allergen is everywhere in your house and triggers asthma in children

The amount of mouse allergen found in the air in many inner-city homes could be high enough to trigger asthma symptoms in the children who live there, say researchers at the Johns Hopkins Children's Center. Their study, published in the February issue of the Journal of Allergy and Clinical Immunology, found more than a quarter of inner-city homes sampled had airborne allergen levels already known to aggravate asthma symptoms in animal research lab workers with mouse allergy.

"Children living in inner-city homes are continuously exposed to the allergy-causing substance found in mouse urine that is circulating in the air," says Elizabeth Matsui, M.D., a pediatric allergist at the Johns Hopkins Children's Center and lead author of the study. "This exposure increases their risk for developing allergic sensitivity to mice, just as it does for laboratory workers who constantly work with rodents."

Other common household allergens known to affect asthma include proteins shed by cockroaches, dust mites, furry pets and mold, along with tobacco smoke and certain chemicals. While previous studies have examined exposure to settled dust mouse allergen in inner-city homes, this is believed to be the first to describe airborne mouse allergen levels.

Once sensitized, such children exposed to airborne mouse allergen at the high levels found in the study may be more likely to experience asthma symptoms, including wheezing or difficulty breathing, which could lead to a full-blown asthma attack or other asthma-related illnesses, Matsui said. "Because asthma attacks have the potential to be life-threatening, these findings are of some concern," she adds.

The researchers report airborne mouse allergen was most likely to be found in homes with cracks and holes in walls or doors, exposed food in the kitchen, or evidence of mouse infestation, such as droppings. Although mouse allergen is most prevalent in inner-city homes, Matsui says previous studies have also detected it in approximately 75 percent of middle-class suburban homes.

"One of the best ways parents can manage their child's asthma is to control the home environment and remove any asthma triggers, including mouse allergen," she adds. "They can do this by sealing cracks and holes in doors and walls, thoroughly disposing of all food remains, and having pest exterminators treat their home."

In the study, Matsui and colleagues collected air and dust samples from the bedrooms of 100 inner-city children with asthma and found 84 percent of bedrooms had detectable levels of mouse allergen. In 25 percent of these bedrooms, airborne levels of mouse allergen were 0.10 nanograms per cubic meter or higher, comparable to what is seen in mouse research facilities. All study participants were also tested for mouse and other allergies, and nine children were found to be sensitized to mouse and 69.7 percent of children had at least one positive skin test to other common indoor and outdoor allergens.

"Unfortunately, many clinicians do not take mouse allergen into consideration when evaluating inner-city children with asthma," Matsui says. "Testing these children for mouse allergy needs to become as routine as testing for allergies to cockroach or dust mites, and clinicians need to be ready to recommend aggressive extermination of mice or other ways parents can control the home environment."

Asthma affects approximately 15 million people in the United States, about a third of whom are children. It is the third-ranking cause of hospitalization for children 15 years and younger and is the leading cause of chronic illness among children. Researchers estimate that asthma is twice as common in the inner city in comparison to other areas.

The study was sponsored by the United States Environmental Protection Agency, National Institute of Environmental Health Sciences, and the National Heart, Blood, and Lung Institute. Co-authors include Elinor Simons, Arlene Butz and Peyton Eggleston from the Johns Hopkins Children's Center; and Timothy J. Buckley and Patrick Breysse from the Johns Hopkins Bloomberg School of Public Health.