Dr. Rob McConnell, professor of preventive medicine at the University of Southern California's Keck School of Medicine, did a study looking at the link between chronic cough, phlegm production (bronchitis) and dog and cat ownership in 475 children.
The asthmatic children were from southern California and were involved in the Children's Health Study, "a longitudinal study of air pollution and respiratory health."
The scientists say that children with pet dogs had "significantly increased cough, phlegm production and bronchitis responses to the measured pollutants, including nitrogen dioxide, ozone, particulate matter and acid vapor."
In contrast, no increases were observed in kids who lived in homes where there were no pets or where there were only cats.
McConnell tells Asia News International, "Cats are highly allergenic, and children with asthma are often allergic to cats. Therefore if an allergen were enhancing the lung's response to air pollution, we'd be more likely to see an association with cats. But in this study we see an effect of air pollution in homes with dogs, so we think endotoxin exposure is a more likely explanation for our results than allergen exposure."
Endotoxin is produced by bacteria and is released upon destruction of the cell walls. When they are inhaled, it causes an inflammatory response in the lungs, and may cause airways to constrict.
McConnell says, "There's experimental literature that shows both allergens and endotoxin interact with air pollution and increase the effect of each other. But there's been very little study to see if these experiments have relevance for the general population of children with asthma."
He concludes, "Further work is needed to determine what it is about dogs that may increase an asthmatic child's response to air pollution."
The new study is in the online edition of "Environmental Health Perspectives."
