For the past couple of decades researchers have been looking at the role that pets, especially dogs, have to play in rates of allergies in children. Many have found that, what is being termed the hygiene hypothesis, is indeed correct, meaning that a little dirt early in life helps to stave allergic diseases, including obesity.
A new study by Anita Kozyrskyj a pediatric epidemiologist of the University of Alberta in Edmonton, Canada, found further evidence of this dog-human linkage and how this lessens the development of everything from obesity to asthma.
Starting in 2013 she wondered if she could pinpoint what and how this might be happening. Her team collected fecal samples from 4-month-old infants in the Canadian Healthy Infant Longitudinal Development (CHILD) pilot study. Of the 24 respondent infants, 15 lived in house with at least a dog or cat.
What they found was that within the households with pets, the children had a higher diversity of microbes in their guts. Microbes, as we now know, can be a good thing for our gut microbiome and immune systems actually develop alongside our gut’s “germs.” Meaning that if babies grow in a more “sterile” pet-free environment, they would be more unprepared to “fight” germs as they grow up.
Kozyrskyj noted, "The abundance of these two bacteria (Firmicutes microbes) were increased twofold when there was a pet in the house," and added that the pet exposure was shown to affect the gut microbiome indirectly—from dog to mother to unborn baby—during pregnancy as well as during the first three months of the baby's life.
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Also interestingly, this study suggested that the presence of pets in the house reduced the likelihood of the transmission of vaginal GBS (group B Strep) during birth, which causes pneumonia in newborns and is prevented by giving mothers antibiotics during delivery.
Kozyrskyj’s study confirms and expands on the work that many other researchers have shown that some “dirt” can be beneficial and help to ward off disease. Including one, conducted at Kuopio University Hospital in Finland in 2012, that concentrated on infants during their first year, and investigated the effect of contact with dogs on the “frequency of respiratory symptoms and infections.” Information about the length of time a dog spent indoors was also gathered, and turned out to be one of the key indicators.
The results were eye-opening. Children with dogs at home were healthier overall, had fewer infectious respiratory problems, fewer ear infections and were less likely to require antibiotics. Researchers considered these results supportive of the theory that children who live with dogs during their early years have better resistance throughout childhood. They also found that the effect was greater if the dog spent fewer than six hours inside, possibly because the longer dogs are outdoors, the more dirt they bring inside with them. The more dirt, the more “bacterial diversity.” This diversity is thought to have a protective influence by helping the child’s immune system to mature — that is, respond more effectively to infectious agents.
Then a 2013 study conducted by the University of California, San Francisco, and the University of Michigan, Ann Arbor, found that living with dogs may prevent children from developing asthma. Mice fed a solution containing dust from homes with dogs developed a resistance to respiratory syncytial virus (RSV), a childhood airway infectious agent. RSV, which is common in infants, is linked to a higher risk of childhood asthma. According to Dr. Susan Lynch of the study team, “Exposing the gastrointestinal tract to pet dust and other microbes early in life prepares it to respond appropriately to a variety of invaders. But since our modern lifestyles involve living in immaculate houses, our immune systems often overreact instead.” Early childhood is a critical period for developing protection against allergies and asthma, and exposure to pets can help.
The idea that our microorganisms may to some extent be collectively beneficial is intriguing. People and dogs have been exchanging microbes for at least 30,000 years, since the first little cave girl kissed the first proto-dog puppy smack on the muzzle. That’s a long history of sharing. It’s possible that our microorganisms are at least symbiotic, and perhaps even played a role in the dramatic domestication of the dog.
As was reported in Nature: Researchers suspect that our long association with canines means that human and dog microbiomes may have developed in tandem. The microbiome of a baby growing up without a dog (and of a puppy growing up without a human) is, in a sense, incomplete. “All of the people alive today probably had ancestors who lived in tribes that hunted with dogs,” says Jack Gilbert, director of the Microbiome Center at the University of Chicago in Illinois.”
Since 2013, Canadian researcher, Kozyrskyj has expanded her pilot study from 24 to 746 infants, around half of whom were living in households with pets. Her team then compared the babies' microbial communities.
The results were basically the same, microbial life flourished in the infants living with pets. And not only that but the “team was now able to show that babies from families with pets (70% of which were dogs) had higher levels of two types of Firmicutes microbes — Ruminococcus and Oscillospira, which have been associated with a lower risk of allergic disease and leanness, respectively.
“Pet exposure can reduce allergic disease and obesity” later in life, added Hein Min Tun, a veterinarian and microbial epidemiologist and a member of Kozyrskyj’s research team.
And while it might be too soon to predict how this finding will play out in the future, they don’t rule out the concept of a “dog in a pill” as a preventive tool for allergies and obesity. Or, as we much rather see, “dog as the pill.”