Parents who see mice scurrying across their floor should be worried about more than just an impending scream from their children. Mouse allergen, in the form of mouse urine or dander, is widely distributed in the inner city and may be a significant contributing factor to the childhood asthma epidemic in urban areas, according to two studies by Johns Hopkins researchers published in the December issue of the Journal of Allergy and Clinical Immunology.
"Before these studies, mice weren't widely recognized as an allergen in homes," says Robert Wood, associate professor of pediatrics and lead investigator of both studies. "Now we know that houses are full of it, and we were surprised that mice turned out to be even more important in inner-city asthma than cats, dogs or dust mites. While cockroach is the more important inner-city allergen, mouse is second in line. Doctors need to take mouse allergen into account when evaluating kids with asthma."
In a study of eight cities, the scientists discovered that 95 percent of all homes in the study had mouse allergen in at least one room; Baltimore topped the charts with 100 percent. Eighteen percent of the children were allergic to mice, and those children tended to have more severe asthma. Finally, they found that the more a person was exposed to mice, the greater the chances that future rendezvous with these rodents would cause a reaction.
For several years, researchers have known that cats, dogs, dust mites and cockroaches can cause allergies that trigger the wheezing and constricted airways of asthma. But while doctors have treated people who work with mice in laboratories for allergies to the furry creatures, until now, not much was known about mouse allergy in the general population.
To fill this knowledge gap, Wood and his colleagues turned to data from the National Cooperative Inner-City Asthma Study, a multicenter study of 1,528 children. First, the researchers analyzed dust samples from the homes of 608 children. Ninety-five percent of these homes had detectable mouse allergen in at least one room, with the highest levels found in the kitchen, followed by the bedroom and television/living room. Eighty-seven percent of the samples from each room in the study had detectable mouse urine or dander.
The researchers then set out to examine the effects of this common allergen. Of the 608 children, 499 had undergone puncture skin tests for all sorts of allergy, including cockroaches, mice, grasses and cats, and came from homes with adequate dust samples. The remainder of homes did not have large enough samples because of superior cleaning skills or difficulty getting dust from noncarpeted floors, or because dust had been used up during other tests. "We found that 18 percent of these children had mouse allergy, and there was a connection between the allergy and asthma severity," Wood says.
Wood and his colleagues recommend that doctors begin evaluating asthmatic children for mouse allergy. "Currently, it is not routine to test asthmatic children for allergies to mice," Wood says. "We think that doctors need to change their approach to inner-city asthma and take this into account. We need to test for this allergy, ask families about mouse infestation, and recommend aggressive extermination of mice just like we do for cockroaches."
The researchers next plan to broaden the scope of their investigation to include suburban homes and non-inner-city environments. They also will continue to define its clinical significance.
Asthma affects approximately 15 million people in the United States, 5 million of whom are children. Nationally, it is estimated that more than 7 percent of children now have the disease. Researchers estimate that asthma is twice as common in the inner city in comparison to other areas.
The NCICAS study consists of 1,528 children, ages 4 to 9 years, from eight major inner-city areas: Baltimore; Washington, D.C.; the Bronx and East Harlem, both in New York City; St. Louis; Chicago; Cleveland; and Detroit. The children were diagnosed with asthma and lived in neighborhoods where 30 percent or more of the households had incomes below the 1990 poverty level.
Both papers were authored by the same group of colleagues and include Peyton Eggleston, co-lead investigator and professor of pediatrics; Wanda Phipatanakul, postdoctoral fellow in pediatrics; Elizabeth C. Wright; and the National Cooperative Inner-City Asthma Study. NCICAS is funded by the National Institutes of Health, Environmental Protection Agency and Center for Indoor Air Research.
For more information about asthma and allergy research at Johns Hopkins, visit http://www.hopkins-allergy.org.