If you have a pet in your home, then you know there is considerable interaction between you, your home environment, and your fur babies. Although companion animals provide us with so much happiness and are known to reduce our stress and improve our mental health, we still are only scratching the surface of how they impact all areas of our health. 

Animals provide us with unique microbial exposure – fur and hair dander that might get washed only once a month, tongues that lick just about anything, paws that touch the outside world and inside our homes, toys everywhere, and copious amounts of pet waste, all of which touch our skin, get on our food and in our mouths, and ultimately end up in our gastrointestinal tract.  

With nearly 70 percent of Americans caring for at least one companion animal in the home, here we explore some of the unique effects (both good and bad) your furry friends might be having on your gut microbiome.

Did you grow up with a pet?

As a newborn baby, microbial colonization of the gastrointestinal tract is an essential process, because what happens in early life has a significant impact on future health. Although many households avoid animals for hygiene, safety, asthma, or allergy reasons, research shows pet exposure in early life can provide a beneficial and tolerogenic environmental effect on the gut microbiota in infants.1 Early exposure to a household pet appears to stimulate a child’s immune system, such that it's less likely to become overly sensitive later in life. 

In a study of 750 infants, mothers who lived with a household pet during their second and third trimesters and for three months postpartum had babies with a twofold greater likelihood of a higher abundance of Oscillospira and/or Ruminococcus in their gut microbiomes, which are inversely associated with childhood allergies, asthma, and obesity.2 The majority of these household pets were dogs and cats.

A small study of 24 infants had mixed results.3 Three-month-old babies with a household pet had higher microbial richness and gut diversity, but also had higher amounts of the following:

  • Clostridiaceae, a family of bacteria known to be associated with poor skin health 
  • Veillonella – especially true in those who had dogs; generally, a bug you want in lower levels
  • Peptostreptococcaceae, a slow-growing family of bacteria that is increasingly resistant to antimicrobial drugs
  • Coprococcus, a generally good bug
  • Those who had cats had lower levels of the good, health-promoting Bifidobacteriaceae
  • Those with dogs tended to have lower Eggertella – a generally bad bug you want to be in lower abundance

A meta-analysis that pooled 11 studies involving 22,000 children and ownership of dogs, cats, birds, and/or rodents during the first two years of life found no association with asthma, but did conclude that being around household pets during the first two years of life is associated with reduced likelihood of airborne allergies.4 Gut microbiome data was not reported in this analysis.

There is good evidence to suggest early exposure to dogs positively impacts atopic dermatitis, also known as eczema, in children. Scientists believe the beneficial genus Bifidobacterium, specifically the transfer of species B. pseudolongum and B. thermophilum from animals to humans, are the microbes of importance in this case.1

Do you have a companion animal now?

In a recent study comparing 214 cat owners to non-cat-owners, researchers found significant differences in gut microbiome samples they attribute to the presence of the felines. Adults with cats had significant decreases in Proteobacteria (a phylum often associated with unfavorable health conditions) and families Alcaligenaceae (generally considered harmful; contains the genus Bordetella) and Pasteurellaceae (generally pathogenic to animals and associated with infections in humans). On the other hand, Enterobacteriaceae and Pseudomonadaceae (both associated with increased risk for intestinal hyperpermeability) were significantly increased.5 

In addition, 50 metabolic pathways were predicted to be changed significantly in the cat-owning group, while 21 and 13 metabolic pathways were significantly changed in the women and men who owned cats, respectively.5 There is a lot to unpack in a study like this, because pathways are complex, and researchers think that because cats are typically indoor animals, it could play a role in the findings.

Be aware there are a few viral, fungal, bacterial, and parasitic illnesses that can be passed from animals to humans. These so-called zoonotic infections can generally be cleared with accurate diagnosis and modern medicine. A few common ones include:

  • Brucellosis – a bacteria you can become infected with by contact with an infected dog. It can cause flu-like symptoms and take 1-2 weeks for symptoms to appear. 
  • Campylobacteriosis – bacteria spread through dog and cat feces that typically results in gastrointestinal-related symptoms in as soon as two days after exposure. 
  • Ringworm – a fungal disease spread from dogs and cats to humans from surfaces with the fungus. Ringworm looks as it sounds: a circular, itchy, red rash on the skin. 

What about general surfaces around the home?

The presence of dogs and cats can impact the home environment too. In a study examining the microbial composition of house dust, bacterial community richness (the number of bacterial taxa present), evenness (relative distribution of taxa in communities), and diversity (calculated using richness and evenness) were increased in all dog-owning households and a subset of cat-owning households. What is extremely interesting is that dust in the homes with dogs had fewer fungal species, suggesting that, in some cases, dogs might have some protective effect against these microbes.6

Although pets contribute to a wide variety of microbes in the household, they are not responsible for them all. Studies of individual bacterial taxa have found that the nefarious genus Pseudomonas is most often present in high-trafficked kitchen and bathroom sinks.7 These bacteria increase the risk for intestinal permeability and inflammation. 

Other research has found certain bacteria present on shower curtains and other surfaces that are rarely found in other areas of the home.8 What the area is used for, number of people in the home, frequency of cleaning, and the humidity, temperature, and light exposure of the area in question factor into what can live, multiply, or die.

The consensus is we share common gut microbiota with the pets and environments around us, and they do indeed influence our health and well-being.

Many of the microbes from these research studies are normal inhabitants of the gut, and an increase or decrease in abundance doesn’t necessarily mean you will experience a change in your health. It is perfectly normal to see changes in taxa with every environmental exposure and lifestyle habit we have. The key to maintaining gut health is about balance and aiming for more of the good bugs and less of the bad ones.

There is still much more to learn about the impact of household pets on the human microbiome and what factors influence their effects – breed, fur length, indoor versus outdoor, whether they go to daycare – might all play a part. 

It is our duty to keep our pets healthy, which includes ensuring adequate exercise, plenty of clean water, a healthy diet, managing proper oral hygiene, maintaining a healthy weight, stimulating their brains, and helping to manage their stress so their own microbiome can thrive. Look to ThorneVet, a division of Thorne, for high quality nutritional supplements for companion animals.

If you want to see how your lifestyle and environment affect you, then take Thorne’s Gut Health Test and learn how balanced your gut is and how to optimize it. 

References

  1. Nermes M, Endo A, Aarnio J, et al. Furry pets modulate gut microbiota composition in infants at risk for allergic disease. J Allergy Clin Immunol 2015;136(6):1688-1690.e1.
  2. Tun HM, Konya T, Takaro TK, et al. Exposure to household furry pets influences the gut microbiota of infant at 3-4 months following various birth scenarios. Microbiome 2017;5(1):40.
  3. Azad MB, Konya T, Maughan H, et al. Infant gut microbiota and the hygiene hypothesis of allergic disease: impact of household pets and siblings on microbiota composition and diversity. Allergy Asthma Clin Immunol 2013;9(1):15.
  4. Lødrup Carlsen KC, Roll S, Carlsen KH, et al. Does pet ownership in infancy lead to asthma or allergy at school age? Pooled analysis of individual participant data from 11 European birth cohorts. PLoS One 2012;7(8):e43214.
  5. Du G, Huang H, Zhu Q, Ying L. Effects of cat ownership on the gut microbiota of owners. PLoS One 2021;16(6):e0253133.
  6. Fujimura KE, Johnson CC, Ownby DR, et al. Man’s best friend? The effect of pet ownership on house dust microbial communities. J Allergy Clin Immunol 2010;126(2):410-412, 412.e1-e3.
  7. Remold SK, Brown CK, Farris JE, et al. Differential habitat use and niche partitioning by Pseudomonas species in human homes. Microb Ecol 2011;62(3):505-517.
  8. Kelley ST, Theisen U, Angenent LT, et al. Molecular analysis of shower curtain biofilm microbes. Appl Environ Microbiol 2004;70(7):4187-4192.