From Our 2007 Archives

Cats Can Hamper Breathing Even in Non-Allergic

By Carolyn Colwell
HealthDay Reporter

MONDAY, July 2 (HealthDay News) -- Adults plagued by allergies can be affected by cat dander even if they aren't specifically allergic to felines, a new European study shows.

"Exposure to cats is more of a problem than was thought," said study author, Susan Chinn, a professor of medical statistics at the Imperial College, London.

Chinn, along with colleagues at 20 European centers, expected to find higher bronchial (airway) responsiveness in research subjects who were sensitized to cats.

What they didn't expect to find -- but did -- was a similar increase in airway reaction among subjects who weren't allergic to cats but were sensitive to three other common allergens: dust mites, mold or timothy grass.

"Bronchial responsiveness is a measure of the propensity of the airways to constrict," Chinn explained. "Although it's not synonymous with asthma, it is an indicator of airways [that are] likely to show an asthmatic response," she said.

Consequently, the study found that "cat allergen exposure at moderate levels may be harmful" to all adults with allergies, regardless of what their allergy triggers might be, Chinn said. "The clinical implication is that it is insufficient to test patients with asthma for cat sensitization," she said, since all allergic people "might benefit from reduced cat exposure."

The findings are published in the first July issue of the American Journal of Respiratory and Critical Care Medicine.

Simply having a cat in the house is a good example of moderate exposure, Chinn said, but it's not necessary. That's because even the presence of cats kept by others in the nearby community was enough to leave cat allergens in mattress dust from homes tested by researchers, she said.

Still, the study's findings would have to be replicated before the researchers could make any strong recommendations about cat ownership, Chinn added.

But Dr. Jerry Shier, an allergist and an assistant clinical professor at George Washington University School of Medicine, in Washington, D.C., said that the European study is likely to spur additional research. That may lead allergic patients to lend more weight to their doctor's recommendations against pets -- even if "they aren't yet allergic to animals yet," he said.

Shier also suggested that schools and other public places where cat and other allergens are likely to be present should give more attention to cleaning hard surfaces and avoiding carpeting.

He noted that cat allergens are particularly widespread because they are "stickier," smaller and lighter than other allergens, which makes them easily airborne. As a result, a person could be exposed without being in the presence of cats. That's why Chinn's group found cat allergen to be ubiquitous in the mattress dust of both cat owners and non-owners.

What makes people with allergies who are not allergic to cats still sensitive to the animals' allergens? No one is quite sure.

The question deserves "a closer look," said Dr. Marc Riedl, an assistant professor of medicine at the David Geffen School of Medicine at the University of California, Los Angeles. One reason cat allergens may have a wider impact is that these small airborne particles, which can be a quarter of the size of dust mites, "are much more likely to have access to the lung than other allergens," he said. Consequently, cat allergens could have wider effects that have nothing to do with allergic sensitivity per se.

Then there are substances called endotoxins. Endotoxins break down portions of bacteria that in turn stimulate the immune system, Shier explained.

The study raises the question of whether endotoxins -- which have been found at higher levels in cat owners' homes -- might be the cause of increased bronchial responsiveness observed in ostensibly non-cat-allergic people, he said. "There [also] may be some other unknown entity that comes from the cat that may be responsible for triggering the bronchial hyperactivity," he added.

The European study also pointed out gender differences in terms of who is most vulnerable to cat allergy. Among the almost 1,900 randomly selected participants included in the study, men and women turned out to be equally sensitive to cats. However, women had a higher exposure to cat allergens, were more likely currently to own a cat, and were more likely to allow the cat in the bedroom.

Cat ownership also varied by country, ranging from as low as 10 percent of participants in Spain to as high as 35 percent among the British.

SOURCES: Susan Chinn, D.Sc., professor, medical statistics, honorary professional research fellow, Respiratory Epidemiology and Public Health Group, Imperial College London; Marc Riedl, M.D., assistant professor, medicine, David Geffen School of Medicine, University of California, Los Angeles; Jerry Shier, M.D., assistant clinical professor, George Washington University School of Medicine, Washington, D.C.; July 2007 American Journal of Respiratory and Critical Care Medicine

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