Abstract
Early childhood exposures may reduce the risk of sensitization and subsequent asthma. We tested this hypothesis in 815 children surveyed repeatedly over 21 years. The presence of cats or dogs in the home at birth, 3, 5, 7, and 9 years was recorded. Diagnosed asthma and symptoms were determined by questionnaire. Most (78.5%) had a cat before age 9, and 49.8% had a dog. The likelihood of skin test sensitivity to cat was significantly reduced by earlier cat ownership (e.g. at age 5, 10.3% vs. 18.3%, p=0.003). House dust mite sensitization was reduced in those with cat or dog (29.0% vs. 40.0%, p=0.039). Sensitization to any allergen was reduced by dog ownership (e.g. at birth, 36.1% vs. 48.7%, p=0.005). Among those with an atopic family history (mother or father reporting asthma or hayfever), owning pets reduced cat sensitization from 27.9% to 14.9% (p= 0.013), dog sensitization from 10.7% to 4.9% (p=0.061), sensitization to any allergen from 58.5% to 45.1% (p=0.020), and the risk of diagnosed asthma at 9 from 16.2% to 8.0% (p=0.035). We conclude that, particularly among high-risk children with a family history of atopy, early exposure to animals modulates immune responses to animal-specific and other allergens, reducing the likelihood of sensitization and consequent asthma.