Cat Exposure Increases Asthma Risk for Children of Asthmatic Mothers
Scientists are gaining a better understanding of the complex relationship between cat exposure and the risk of developing asthma. For many years, scientists thought that cat exposure increased a child's asthma risk. Recent studies, however, have suggested that exposure to high levels of cat allergen during infancy can actually protect children against developing asthma. This week, a new study supported by the National Institutes of Health (NIH) adds another twist to the developing story.
The new study confirmed the protective effect of cat exposure for at-risk children in all but one situation: when the child's mother has asthma. If the mother has asthma, then a cat in the home actually triples the risk that a child will develop persistent wheezing - an initial indication of asthma - by age five.
"Asthma is a complex disease in which there appear to be many factors, both genetic and environmental," says Marshall Plaut, M.D., chief of the allergic mechanisms section at the National Institute of Allergy and Infectious Diseases (NIAID). "To better understand asthma, we need studies like this one that sort out these factors and define the relationships among them."
"This study is the first to show that the effect of having a cat in the home may depend upon whether your mother has asthma or not," says lead author Juan C. Celedón, M.D., Dr.P.H., who, along with primary investigator Diane R. Gold, M.D., M.P.H., and colleagues conducted the research at Brigham and Women's Hospital in Boston, Massachusetts. Details of this study will be published in the September 7 issue of The Lancet. The research was supported by NIAID and the National Institute of Environmental Health Sciences (NIEHS).
"For years, physicians have been advising families with allergies to stay away from pets," says Dr. Celedón. "However, it appears that for a vast majority of children, being exposed to a cat early in life may be beneficial. That said, there is a subgroup of children - those whose mothers have asthma and, perhaps, those whose mothers are allergic to cats - who should probably avoid cat exposure." Children with documented cat allergy or with asthmatic symptoms triggered by a cat should also avoid cats, he adds.
The study followed 448 children with a family history of allergic diseases from birth to age five. Through periodic telephone interviews with caretakers, the researchers gathered information on the children's exposure to pets and on how often the children experienced episodes of wheezing. In addition, the researchers tested dust samples from each child's home for levels of cat allergen. The researchers then analyzed the data they collected, adjusting for factors such as sex, household income, and day-care attendance.
In the group of children with non-asthmatic mothers, those exposed to a cat were 40 percent less likely to experience persistent wheezing as compared to those with no cat exposure. This risk reduction remained consistent in each of the five years.
In the group of children with asthmatic mothers, however, those exposed to a cat were significantly more likely to wheeze as compared to those with no cat exposure. In fact, the risk of wheezing increased in each of the five years of the child's life. By the third year, the risk of wheezing doubled, and by the fifth year it more than tripled. This finding suggests that the children of asthmatic mothers become more readily sensitized to cat allergen - the first step in developing asthma — and wheeze when exposed to it.
The finding may be explained by genetic influences passed on from the mother, or it may result from environmental influences shared by mother and child, Dr. Celedón says.
The researchers plan to continue following this group of children and to test them for allergies to cats as well as other potential asthma triggers such as cockroaches and dust mites. "We are very grateful to the families for taking the time out of their busy schedules to participate in this important study," says Dr. Gold, primary investigator. "We hope to follow the children into their preteen years to see whether the cat exposure in early life remains protective against wheeze and allergy as the children of the non–asthmatic mothers grow older."
NIEHS is the component of NIH that conducts and supports research on the environmental causes and triggers of disease and our human susceptibility to them.
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Reference: J. C. Celedón et al. Exposure to cat allergen, maternal history of asthma, and wheezing in the first five years of life. The Lancet 360(9335):781-82 (2002).
NIAID is a component of the National Institutes of Health (NIH), an agency of the U.S. Department of Health and Human Services. NIAID supports basic and applied research to prevent, diagnose and treat infectious diseases such as HIV/AIDS and other sexually transmitted infections, influenza, tuberculosis, malaria and illness from potential agents of bioterrorism. NIAID also supports research on transplantation and immune-related illnesses, including autoimmune disorders, asthma and allergies.
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