Growing up around pets is particularly helpful for immune development — here's why
Looking at the striking portraits, he was struck by the number of animals living amidst the Traveller families. It gave him an idea for a new study.
“There were a lot of animals — dogs, cats, ferrets, and always horses,” he says.
Shanahan decided to try to characterise the gut microbiomes of more than 100 Irish Travellers and compare them with those of people in Ireland, Britain, the US, and Canada living more modern lifestyles.
When his study was published in 2020, the results jumped out. “The Traveller microbiome was more akin to what you see from hunter-gatherer tribes in Tanzania or Mongolian horsemen than the rest of the Irish population,” he says.
Shanahan noted that indigenous communities from other countries in the study also lived in close quarters with animals. As he dug deeper into the data, he found that this constant animal exposure seemed to play a key role in their unique microbiome characteristics, more so than other possible explanations, such as diet.
The diversity of their gut microbiomes particularly captured his attention because while Irish Travellers often experience poor physical and mental health, one area — directly linked to gut microbiome diversity — where they fare better than the rest of the population is their immune health.
“I ran a clinic for inflammatory bowel disease, Crohn’s disease, and ulcerative colitis for many years. Based on population averages, I should have seen 40 to 50 Travellers over the years, and I never saw one.”
While one explanation could be that Travellers are often nomadic and can be reluctant to engage with the conventional health system, Shanahan says that this is unlikely to be the full picture. In his view, the apparent lack of Travellers presenting with very serious inflammatory bowel conditions suggests that they probably have better gut health than the average Irish person.
“As a socially marginalised ethnic group, it makes sense that they may not get to the attention of a doctor for things like asthma or allergies or eczema but it must happen if you’ve got Crohn’s disease or ulcerative colitis,” he says. “Those conditions present with bloody diarrhoea, the symptoms are quite dramatic, and it’s life-threatening.”
It seemed to Shanahan that the Traveller microbiome was protecting them against these chronic inflammatory diseases and, somehow, animals were responsible.
While the concept of having pets is largely a modern phenomenon, humans have been domesticating and coexisting alongside animals for tens of thousands of years, and a growing amount of research worldwide is increasingly suggesting that our immune system has evolved to expect to see the presence of microbes from dogs, cats, cows, or horses.
As a result, some scientists now believe that regular exposure to these bacteria throughout life triggers the immune system to develop in ways that are beneficial for our health, preventing it from going awry, as in the case of many autoimmune diseases, and attacking our own tissues.
While you are unlikely to acquire any permanent microbial residents directly from your pet, Shanahan believes that animals can help transfer gut bacteria between different human household members. This increases the diversity of the gut microbiome, making it more stable and better able to withstand harmful pathogens from flourishing.
“We know that dogs can do this,” he says. “If you and I are living in the same house and we both pet the dog, that is a way of receiving and transmitting microbes from each other.”
Due to the benefits for the gut microbiome, enabling children to grow up around pets from the earliest stages of life, and even before birth, is increasingly viewed as particularly helpful for their immune development.
Last month, a major new study found that growing up alongside a pet dog reduces the risk of eczema in children who are genetically prone to the condition.
Children in the Amish communities of North America have previously been found to have significantly lower rates of allergies and asthma as a consequence of living in close proximity to animals.
Similar trends have been seen in children who live on farms in Central Europe.
“There have been some cool studies of kids growing up on these traditional Austrian farms where the cows are in the basement at nighttime, and they don’t get allergies,” says Liam O’Mahony, professor of immunology at APC Microbiome Ireland.
“And, again, it’s that traditional farming, interacting with animals, that seems to be important. The kids who grow up on more modern farms with more machinery and less contact with animals are far less protected.”
Jonathan Hourihane, professor of paediatrics at RCSI University of Medicine and Health Sciences, points out that while pets are sometimes viewed as a potential source of allergies, this is much less likely to be the case if children are exposed to them within their first year of life.
“Exposure is generally now considered to be tolerising,” he says. “The idea that you have to avoid something to prevent an allergy developing has been proven to be incorrect. We’re meant to live with animals, and pets are part of normal family life. It’s good for children’s psychological and social health too.”
While caring for a pet can be expensive, it seems our furry companions can repay the investment in multiple unexpected ways.
According to a new scientific review published earlier this year by psychologists in Australia, pet owners make fewer doctor visits per year. However, the evidence for whether they improve long-term mental health is inconclusive.
The apparent immune benefits may further swing the dial in favour of pet ownership — but are there any particular dos and don’ts?
According to O’Mahony, whether you choose to let your cat or dog sleep on your bed really comes down to personal preference. However, he says it’s still generally important to maintain good hygiene practices and make sure that your animals are up to date with all their vaccine requirements.
“It is very important to keep pets vaccinated, wormed, and free from fleas as this protects your pet and you from dangerous pathogens and infectious diseases that can be very harmful,” he says.
“Likewise, with hygiene, a balanced approach is needed.
“We know excessive cleaning can be detrimental but there is a sensible minimum level that should be maintained, for example, correct disposal of poo in the bin is important to prevent disease.”
And what about children who grow up without the presence of pets? Last year, a research group from Italy published data that suggests it may be possible to replicate some of the benefits by allowing them to regularly interact with animals in other settings such as zoos or during farm visits.
In the study, in which children from homes with no pets were allowed to regularly pet horses under supervision, subsequent gut microbiome testing showed that their microbiomes began to produce more beneficial chemicals for immune health.
It seems likely that having a pet at any stage of your life could yield all kinds of health benefits.
“While there is a critical immunological developmental window in early life where we think these microbial exposures have the most significant effects on the immune system, “ says O’Mahony, “living with animals during adulthood remains important and will likely continue to provide immune health benefits.”
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