Dog Exposure in Infancy Decreases the Subsequent Risk of Frequent Wheeze but Not of Atopy

Abstract

Purpose of the Study. Asthma is on the rise, and pets are a variable that may influence the TH1/TH2 response in infants and children. This study’s objective was to determine whether pet exposure, specifically dog, early in life alters the risk of frequent wheezing (>3 times per year) or allergic sensitization.Study Population. Cohort of 1246 healthy infants as part of the Tucson Children’s Respiratory Study were enrolled at birth and followed until age 13 years of age.Methods. Evaluations performed at birth and ages 2, 3, 6, 8, 11, and 13 years provided information regarding pet exposure, parental asthma, frequency of wheezing, and skin test sensitization. Confounding variables including smoking, day care, number of siblings, cat exposure, and ethnicity were also considered.Results. From the original cohort of 1246 subjects, data regarding wheezing and pet exposure was obtained from 1076 (86%) of participants through age. Frequent wheezing was seen in 237 (22%) of the study population. Almost 400 (32%) subjects had indoor dogs. Overall, children had significantly less wheezing if they had a dog versus those children that did not have a dog (17.1% vs 24.6%), but this reduction was mainly seen for children without paternal asthma. Wheezing reduction occurred regardless of the child’s atopy state. In children with parental asthma, there was no greater or lesser risk of wheezing based on the presence or absence of a dog. However, if the dog was removed at either age 3 or 6 in children with or without parental asthma, the child’s risk of wheezing increased. Dog skin test sensitivity was unaffected by the presence or absence of a dog in the home.Conclusion. The presence of a dog in the home may reduce the risk of developing asthma.Reviewers’ Comments. It is important to understand that this study did not focus on asthmatic children who are already sensitized to or symptomatic with exposure to dogs. In general, children with parents without asthma are less likely to develop asthma, but the presence of a dog is associated with an even lower asthma frequency. More interesting is that if the dog was removed during early childhood, the risk of developing frequent wheezing increased. Neither frequent wheezing in children with parental asthma, nor development of a positive dog skin test appear to be affected by the presence of a dog. This is another piece of evidence supporting the hygiene hypothesis and may suggest that early exposure to endotoxin, through pet exposure, may protect against asthma.