For some children who live in inner-city areas, exposure to certain pet and pest allergens in infancy may lower the risk of developing asthma by age 7.
A new study published in the Journal of Allergy and Clinical Immunology, that included children living in inner-city St. Louis, Baltimore, Boston, and New York City, also linked a mother’s mental health to her child’s risk of developing asthma.
“This study suggests we may not be focusing on the right targets for preventing asthma in the inner city,” says Leonard B. Bacharier, a professor of pediatrics and an asthma specialist at Washington University in St. Louis. “We may not need to worry about making sure the household environment is maximally clean—in fact, it’s possible that could be counterproductive.
“But helping women manage the challenges of mental health may make a difference.”
Of the 442 children with complete data, 130 (29 percent) had an asthma diagnosis by age 7. Higher amounts of cockroach, mouse, and cat allergens measured in house dust during a child’s first three years of life were associated with a lower risk of developing asthma.
“How can exposure to cockroaches be good for you?”
Children at high risk of asthma included those whose mothers reported having the condition and those with higher levels of a chemical called cotinine measured in umbilical cord blood at birth.
A product of the breakdown of nicotine, cotinine measured in umbilical cord blood is a marker of tobacco use during pregnancy. While smoking before pregnancy or after birth—by the mother or other household members—was not associated with an increased risk of asthma in this study, a mother’s stress and depression, measured via questionnaires, had a significant association.
Of particular interest, is the analysis of the bacteria associated with the allergens, especially the counterintuitive finding that more cockroach exposure is beneficial. In fact, high levels of cockroach allergen offered the most protection against the development of asthma, followed by mouse and then cat allergens.
“These allergens don’t exist by themselves—bacteria live with them,” Bacharier says. “It’s possible that the allergen itself is not the problem. This could help explain data that seem counterintuitive. How can exposure to cockroaches be good for you?
“If the cockroach allergens happen to come with bacteria that are helpful, then you end up being protected. This suggests whole new avenues of studies looking at the household dust microbiome as well as the human microbiome and their interactions in the development of asthma.”
In households where children developed asthma, the bacteria associated with house dust tended to be microbes that cause disease, or their close relatives. In contrast, households where children did not develop asthma tended to have bacteria that have shown evidence of protecting against respiratory problems.
Because the study was observational, researchers can’t say whether certain bacteria or allergens cause or prevent asthma. But the data do point to new areas of research to pursue in determining what leads to the development of asthma in early life and what can be done to prevent it.
The National Institute of Allergy and Infectious Diseases, of the National Institutes of Health (NIH), funded the work through its inner-city asthma consortium. Coauthors are from Boston University School of Medicine; Columbia University; Johns Hopkins University School of Medicine; the University of California, San Francisco; and the University of Wisconsin-Madison.