One aspect of life with dogs is that my house and clothing tend be coated in a layer of hair. However, a recent study by Fujimura et al. indicates that the dust in houses with dogs may confer protection from airway allergens and respiratory infection compared to houses with no pets. Fujimura et al. exposed young mice to dust from two houses, one with a dog (D) and one without (NP). Mice exposed to D dust had significantly reduced immune reactions when triggered and distinct gut microbiome communities compared with those treated with NP dust. Lactobacillus johnsonii was abundant in the microbiome of the mice exposed to D dust, subsequently isolated from the D dust, and shown to attenuate the development of allergic airway responses and respiratory infection in mice. The authors suggest that manipulation of the gut microbiome may offer therapeutic benefits for people with asthma and hay fever.
Dogs are not the only animals shedding microbes that may be beneficial for people. This research builds upon numerous studies (reviewed here) indicating that children who grow up on farms have a lower risk of developing asthma, hay fever and allergic sensitization. Prenatal and early contact with livestock and the consumption of unpasteurized cow’s milk were identified as providing the most effective protective exposures. These studies extend the hygiene hypothesis, proposed by David P. Strachan in 1989, which suggested that allergic diseases became more prevalent in the late 20th century as a byproduct of reduced family size and increased cleanliness. Studies conducted in the intervening twenty years have shown that microbial exposure by “Old Friends” such as Helminths, saprophytic mycobacteria, bifidobacteria and lactobacilli may indeed affect the development of some chronic inflammatory diseases, including type 1 diabetes, inflammatory bowel disease, multiple sclerosis, periodontal disease as well as hay fever and asthma.
Now that I can embrace the dust bunnies in my home, what I’d love to see next is a study showing that dust from houses with dogs that shed confers more microbial benefits than dust from houses with dogs that don’t shed (such as the Labradoodle and the Cockapoo) that are so popular these days. Then we will have yet another reason to encourage our friends to adopt pets from animal shelters.