It wasn’t that long ago that having a family history of allergies meant that the family dog or cat must go. The thought was that their presence would aggravate allergies and that a clean house free of dust and allergens could prevent children from developing allergies. How the times have changed, there is now plenty of research to support the notion that children who grow up with pets have lower rates of asthma and allergies. This research has resulted in the hypothesis that living in a home that is too clean (ie. free of germs and allergens) can actually increase someone’s susceptibility to developing allergic diseases like asthma, eczema, and rhinitis. This hypothesis is called the hygiene hypothesis and has been a hot topic of research for years. The idea is that our immune system needs certain types of microbes present in our body to educate them and help guide the appropriate immune responses. Without them, our bodies overreact to normally harmless things (like dog dander and peanuts).
There currently exists a large cohort study ongoing in Canada called the Canadian Healthy Infant Longitudinal Development Study (CHILD). This cohort consists of 3500 children born after 2010 and their parents. Samples of house dust, food, blood, stool, urine, breast milk, and questionnaires were collected. The goal is to unravel the complexity of asthma and allergies to understand what early life exposures may put someone at risk for developing these diseases. Recently, a group of researchers on behalf of the CHILD study published a paper looking at how exposure to pets in the early stages of life affects the bacteria in the gut of children.
In this study, the researchers collected gut microbiome data (all the microbes in the gut) on 746 infants and asked the mothers whether they had a pet in the house during pregnancy only or during pregnancy and after birth. They looked for associations between owning a pet and certain families of bacteria in the gut. Over half of the children were exposed to a pet at some point as a child, 8% only during pregnancy and 46.8% during and after pregnancy. The levels of two bacteria, Oscillospira and Ruminococcus, were elevated in the guts of children with family pets. The levels of Streptococcaceae were elevated in children who had mothers that took antibiotics but were reduced if those same families had pets present in the house.
We currently don’t have a good idea of how certain families of bacteria interact with the immune system in a good or bad way so it is hard to say whether any given family is good or bad. However, the two families of bacteria present in children with household pets have been associated with a reduced risk of developing allergies and obesity in other studies and so it is possible that they are ‘good’ bacteria here in this study. More work needs to be done to identify how these bacteria are interacting with the developing immune system in babies and how this may increase their risk for allergic disease. It is clear however that the microbiome of children with household pets is vastly different than those without, the question is whether this protects them from allergies and asthma. At this point in time it is too early to say that everyone at risk for asthma should go get a dog but having one in the house certainly doesn’t hurt and in fact could be beneficial. For more reading on the relationship between household pets and allergic disease see this commentary.
Photo Credit: Flickr smlp.co.uk.