Exploring the interconnected world: The relationship between human and pet microbiomes

Sponsored by Hill's Pet Nutrition

Microbiomes—the communities of microorganisms such as bacteria, fungi, and viruses residing in and on various parts of animals and humans and in the environment—are integral to health and disease. In recent years, significant advances have been made in understanding the human microbiome. However, a growing area of research is exploring the microbiomes of pets and the complex relationships shared with the microbiomes of their human counterparts. For veterinary professionals, this interconnected microbiome frontier holds profound implications for both animal and human health.


The human microbiome: A brief overview
Human microbiomes are primarily concentrated in various body niches, including the gastrointestinal (GI) tract, skin, oral cavity, and respiratory system. These microbiomes influence numerous aspects of health, from digestion and nutrient absorption to immune system modulation and pathogen defense. Dysbiosis, or the imbalance of microbiota, is linked to a variety of conditions such as inflammatory bowel disease, allergies, and even mental health issues.¹


Pet microbiomes: An emerging field
Similarly, pets, particularly dogs and cats, harbor diverse microbiomes that are crucial for their overall health. The GI tract of pets is home to complex microbial communities that aid in digestion, nutrient absorption, and immune function. Skin and oral microbiomes play protective roles against pathogenic bacteria infections,^2,3 regulating immune response^4,5 and maintaining homeostasis of the skin and oral cavities.⁶ Understanding pet microbiomes can provide insights into common veterinary conditions such as allergies, GI disorders, and skin infections.


The human-pet microbiome nexus
Pets and humans share several microbiome-associated phenotypes such as obesity, gastric inflammation, and chronic kidney disease. On the other hand, there are microbiome-relevant characteristics special to each host, such as their unique nutritional requirements. For instance, companion animals do not rely on the microbiome for energy production the way humans do, and cats require more protein in their foods compared with dogs and humans, who consume more omnivorous diets.⁷ The microbial communities that assemble in each host environment have evolved to adapt to that host’s physiology and food intake while also playing a role in modulating host processes such as disease and metabolism. Although there are common microbial members residing in the gut microbiome of cats, dogs, and humans, there are also microbial species unique to each host.⁸ Some microbial species that are present in both companion animals and humans carry different genes, which may enable them to perform different metabolic or protective functions. This indicates host-specific evolution of microbes to thrive and contribute tailored functionality to each host.


Microbiome sharing and transmission
Although the amount may differ from one individual to another, it is common for people in the modern era to spend more than 90% of their time indoors.⁹ Humans often share the same living environment with their pets, facilitating the exchange of microbes. Findings from studies have shown that pet owners often share more microbial similarities with pets in their household compared with pets in other households.^10,11 This bidirectional transfer occurs through direct contact, shared surfaces, and even the air.

Companion animals can also be carriers of environmental microbial species, especially those who live both indoors and outdoors. One study looked at the microbial composition in the home environment in homes with dogs, cats, or no pets.¹² Five homes of each type were studied.¹² The homes that had dogs had increased microbial diversity when compared with homes with no pets, and homes with cats fell in the middle in bacterial diversity and richness.¹² This makes sense considering the vast majority of cats spend their time indoors and are not exposed to additional types of bacteria in the outdoor environment.

Often, when we think about the exchange of microbes, we think about the transmission of pathogenic strains such as Clostridioides difficile, Campylobacter spp, or Escherichia coli.^13-15 However, the transmission of commensals, the beneficial or neutral resident microbes, between humans and pets is an emerging field of study due to the potential positive effects of microbe sharing.


Impacts on health
Sharing microbiomes has potential health implications. Pets can contribute beneficial microbes that enhance human microbiome diversity, potentially offering protective benefits against certain diseases.¹⁶ Conversely, pets can also be carriers of pathogenic microbes. Findings from one study discovered that bacterial species causing periodontal disease in the mouth could be transmitted between dogs and humans.¹⁷ As a result, a balanced approach to pet ownership and hygiene is essential.


Microbiome and allergies
There is compelling evidence to suggest that early-life exposure to pets can influence the human microbiome in ways that reduce the risk of allergies, otherwise referred to as immunological priming or the hygiene hypothesis.¹⁸ Pet ownership, particularly of dogs, has been associated with a decreased prevalence of asthma and allergic diseases in children.^18,19 This protective effect is thought to be mediated by microbiome-induced immune modulation. Children who lived with pets in the household had higher microbial diversity of their gut microbiome.^18,20 On the other hand, children who developed asthma by the age of 7 years had a low total diversity of the gut microbiota during their first month of life when compared with children who did not develop asthma.²¹ Therefore, early-life exposure to pets appears to play a role in shaping the human microbiome and potentially lowering the risk of developing allergies and asthma.


Therapeutic potential
The One Health concept emphasizes the interconnectedness of human, animal, and environmental health, with a growing focus on microbiome research. Scientists are investigating how our shared environment affects health, including the roles that pets play. This research holds significant therapeutic potential, such as developing probiotics, prebiotics, and other microbiome therapies such as the use of postbiotics or metabolic products, to enhance human and pet health. It also informs better hygiene and pet care practices, thereby reducing disease transmission risks and amplifying health benefits for both humans and pets. However, close human-pet contact can promote the exchange of antibiotic-resistant bacteria, resulting in hard-to-treat infections.²² This underscores the importance of careful antibiotic use in both human and veterinary medicine. By understanding these dynamics, strategies can be devised to control the spread of resistant bacteria, preserve antibiotic effectiveness, and protect the health of both humans and their pets through focused interventions.


Future directions and research
Microbiome profiling
More extensive and detailed profiles of pet microbiomes across different species and breeds are essential to understanding the full scope of their role in health and disease. Microbiome sequencing, combined with specific experiments, can answer many important questions about pet health. These include:

• What external factors affect the pet’s microbiome?
• How do these factors change the variety and balance of microbes?
• How do different microbes move and spread between the pet and their owner?
• Which specific microbes or groups of microbes are important for keeping pets and their owners healthy?
  

Advances in sequencing technologies and bioinformatics will be pivotal in the effort to answer these questions in our quest to better care for our pets.

Longitudinal studies
Long-term studies tracking the microbiomes of pets and their owners can provide deeper insights into how these microbial communities coevolve and influence health over time. Such research may identify key microbial markers associated with disease prevention or progression.


Conclusion
The intricate relationship between human and pet microbiomes represents a fascinating and highly relevant area of study for veterinary professionals. This interconnected microbial world not only influences the health of pets and their owners but also opens up new avenues for preventive and therapeutic strategies. By embracing this holistic perspective, veterinarians will be able to enhance animal care and contribute to the broader understanding of microbiome health across species. The journey into the enigmatic realm of microbiomes is just beginning, and it promises to bring transformative possibilities for both veterinary and human medicine.


References

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