Tuesday, December 24, 2013

Can dogs protect kids against asthma?

Indoor/outdoor dogs, such as little Chester here, may protect kids against developing asthma.
We hear a lot about people being allergic to animals, but animals may play a role in protecting us against allergies. 

Previous studies have found that exposure to dogs in early childhood is associated with a reduced risk of development of allergic disease, but why? We know that dog owners are exposed to different microbes in house-dust than non-dog owners.

A recent study, published in the Proceedings of the National Academy of Sciences, looked at mice exposed to dust from households where dogs were allowed outdoors.

When those mice were challenged (with ovalbumin or cockroach allergen) they had significantly reduced allergen-mediated airway pathology than mice exposed to dust from a household with no pet, and those not exposed to house dust.

Cheddy runs through the mud.
They hypothesised that something in the dog-tainted dust (or as they call it, dog-associated dust) is protective. The thinking is that dog dust, when ingested, inoculates the gastrointestinal tract with a population of organisms ("the gastrointestinal microbiome"), the net effect of which is to protect against allergic responses. One such organism, the bacteria Lactobacillus johnsonii, was found to be particularly effective, but not as effective as a more diverse microbiome. (The argument is along the same lines as the hygiene hypothesis).

So kids whose folks refuse to adopt a dog because someone might develop an allergy now have some powerful data with which to lobby them. 

On another note, as someone who does not suffer from allergies to pets or dust, I've never paid too much attention to the literature, but I was fascinated to learn that the burden of chronic inflammatory disease such as asthma is increasing at a rate of knots in Western nations, and may be associated among other things with our indoor lifestyles. House dust and its contents have much to answer for here.

The authors cited one study which found that we spend around 92% of our time indoors (which is where we get most of our environmental microbial exposure). Its a timely reminder to go outside, and if you have an exclusively outdoor dog remember that they could be getting only a slice of that remaining 8% of your time - a sobering statistic!

Sleeping it off after a bath. Chester relishes his indoor time.

Fujimara KE, Demoor T, Rauch M, Faruqi AA, Jang S, Johnson C, Boushey HA, Zoratti E, Ownby D, Lukacs NW & Lynch SV (2013) House dust exposure mediates gut microbiome Lactobacillus enrichment and airway immune defense against allergens and virus infection. PNAS