Dogs, Microbiomes, and Asthma Risk: Do Babies Need a Pet?

Cautious new parents may instinctively avoid letting their infants get down and dirty with the family dog.

But research from Sweden shows such interactions—dog slobber, dander, and muddy paws included—may actually decrease the risk of infants later developing childhood asthma.

The new study, “Early Exposure to Dogs and Farm Animals and the Risk of Childhood Asthma,” published in the Journal of the American Medical Association Pediatrics (JAMA Pediatrics), November 2, looked at the incidence of childhood asthma in children who were raised in homes with pets or on animal farms in their first year of life. Lead author Tove Fall, PhD, of the Department of Medical Sciences, at Uppsala University in Sweden, and colleagues completed a prospective study with a large sample size found a 13% lower risk [odds ratio 0.87] for developing asthma in children who were exposed to dogs as babies, and a 52% lower risk [odds ratio 0.48] if the babies were around farm animals.

The study builds on a growing body of information that the microbiomes of dogs and humans have some organisms in common, and that they tend to share them when they live together.

Researchers at the University of Colorado at Boulder (UCB) found that “dog ownership significantly increased the shared skin microbiota in cohabiting adults, and dog-owning adults shared more ‘skin’ microbiota with their own dogs than with other dogs,” in an article published online two years ago.

Rob Knight of the UCB’s department of chemistry and biochemistry and colleagues collected and analyzed microbes taken from dogs and their human companions and cataloged them.

Think a dog’s mouth is clean? Define “clean.”

In the article, Knight wrote, “Whereas human skin tends to be dominated by a few taxa at relatively high abundance (namely Propionibacteriaceae, Streptococcaceae and Staphylococcaceae), dog paws and forehead harbor a more even mixture of taxa commonly found in a variety of host-associated environments including mammalian gut (Enterobacteriaceae, Fusobacteriaceae), mouth (Porphyromonadaceae, Veillonellaceae), and skin (Propionibacteriaceae, Staphylococcaceae), as well as free-living environments such as soil and water (e.g.., Hyphomicrobiaceae and Sphingomonadaceae.

But until the Swedish study, there was little proof that sharing microbes had a measurable benefit.

The study was feasible in part because In Sweden, dog owners have been required to register their dogs, with either an ear tattoo or a microchip, since 2001, meaning there are better records regarding dog ownership than in many other countries. About 80% of dog-owners comply, the authors wrote. The researchers used several nationwide birth registers to get data on births, then looked at two other registers to find asthma patients. Those were the Swedish National Patient Register and the Swedish Prescribed Drug Register.

There were 1,011,051 children born between January 1, 2001 and December 31, 2010. The researchers defined exposure to dogs as “having a parent registered as a dog owner during the child’s whole first year of life.” The study also included children whose parents were registered as being “animal producers or related workers” in the Swedish Longitudinal Integration Database for Health Insurance and Labour Market Studies.

According to the results, “Dog exposure during the first year of life was associated with a decreased risk of asthma in school-aged children” even when the researchers adjusted for potential confounders. The results were true for children whose parents had asthma, for first firstborn children, and when alternative definitions of asthma were used. Exposure to farm animals showed “a notably reduced risk for asthma.”

It may seem counter-intuitive that pet ownership could reduce the likelihood of children developing asthma, but in an interview, Fall cited the hygiene hypothesis, which posits that some infectious organisms protect humans from autoimmune disorders.

For that reason, the theory goes, the human immune system benefits from being around animals due to the sharing of some normal bacterial flora.

“Exposure to dogs in early life may be beneficial during normal immune maturation,” he said.

While the news may surprise parents, physicians and scientists should take the findings in stride. “Physicians won’t be too shocked” by the results, said James Schmitt, DO, a pediatrician with Sentara Pediatric Physicians in Elizabeth City, NC, “The hygiene hypothesis as it applies to allergies is well-known,” he added, and allergies go hand-in-hand with asthma, as well as with eczema.” If a young child’s exposure to potential allergens such as those in animal dander prevents allergies, it should also help prevent asthma.

Lena Van Horn, DVM, of the Signal Mountain Veterinary Clinic in Tennessee, agreed, adding “I think this is something we knew was going to be proved, we just didn't’t have much science on it yet.”

Kids and pets do seem to naturally go together, and Van Horn said, “The immune system doesn't’t work unless it is educated.” Having a pet teaches the immune system “what it is not to be human,” she said.

Fall concurred, but added that one aspect of the study surprised him: “I was surprised to see that asthmatic parents in Sweden do not seem to avoid pet ownership, and I am glad to be able to comfort them that the same risk reduction is seen for their children.”

A secondary finding of the study, which Fall described as a “quite crude analysis,” is that while early exposure to dogs appears to decrease the risk of asthma, it may increase the risk of pneumonia. It could be that the exposure to certain microorganisms and the fact the children’s immune systems are still developing play a role in that finding. Dr. Fall says “further analysis is needed” before any conclusions can be drawn.

As for what this study might mean in practice, both Fall and Schmitt say that the results can serve as a way to alleviate worries new parents may have. Schmitt said he has shown concerned parents other studies that concluded dog exposure may reduce childhood allergies.

“My take-home message from this study is that parents at this point do not need to worry about keeping their dog or getting a puppy when expecting a baby for fear of asthmatic disease.”

There are several areas for potential future research. Fall says he would be interested in seeing “studies with randomized interventions of dog and farm environment exposure in children,” and Schmitt is curious about the possible link between pneumonia and early exposure to dogs.

Belgian researchers have looked at the benefits of breathing “farm dust” in childhood.

They even raised the interesting possibility of locating day-care centers on farms.

Despite the good news in the study, there are caveats, such as it is important to make sure pets are not carrying parasites. “You can get worms from your dog,” said Van Horn. “You do still have to be wary and make sure the pet is healthy, of course.”

Fall cautioned that the recommendation to get or keep a dog “is valid only for families without a child already having allergies.” He adds that while having a pet is “likely to enrich the family life in many ways, and perhaps also enriches the child’s microbiome and immune system” it does not come with a guarantee that all children who cuddle up with canines will be asthma-proofed.