It is well documented that the incidence of allergy and asthma is rising in recent years. Although this is true for all age groups, it is most particularly evident among adolescents. One theory about the factors leading to this increased susceptibility to hay fever, wheezing, and asthma has been that we are not accumulating the proper exposure to allergens at a young age. To further investigate this proposal, a recent study from Canada concentrated on the impact of pet exposure during pregnancy and infancy and the subsequent development of childhood allergies and asthma. The result is good news for pet lovers, especially furry ones.
Research data now shows that exposure to furry pets such as dogs and cats during a critical immunological window early in life was associated with an increasing abundance of particular gut microbes that have been associated with lower risks of allergy, atopic dermatitis, asthma, and even obesity.
The mechanism relates to alterations of the infant gut microbiome during a crucial developmental window. The microbiome is a term that is used to encompass the enormous variety of microbes that inhabit various parts of our body, such as the gut, skin, or respiratory system. These include bacteria, fungi, and viruses.
The colonization of our gut by microbes is an essential aspect of our life cycle and influences every developmental stage. The neonatal period and infancy are now understood to be a critical crossroad for the accumulation of microbes that will affect the remainder of our lives. Pet ownership is among several of the environmental factors that are known to contribute to this crucial process.
The Canadian study concentrated on the influence of furry pets on the infant gut microbiome from exposure to them during the second and third trimesters of pregnancy extending across the first 3 months of life. Their research documented that there was a significant increase in the bacterial strains known to be associated with lower incidences of childhood allergy, asthma, and childhood obesity in infants that were exposed to pets in utero and in the neonatal period compared to those that were not.
It was surprising to find that even if the pet was given up for adoption just before birth, the infant gut microbiome was still affected. And that positive influence was sustained even under some of the circumstances that are clinically associated with lowered neonatal immunity, such as cesarean section birth and antenatal antibiotic usage. The effect was still present even if the child was not breastfed. In addition, the researchers also found a decreased rate of transmission of group B Streptococcus in infants, a bacterial strain as that has been associated with neonatal pneumonia.
The hygiene hypothesis
This entire line of research is related to what has been termed the “hygiene hypothesis”. This was a concept that originated in 1989 and has been subsequently supported by a number of epidemiological investigations. Researchers noted that there has been a significant increase in allergy and asthma in the populations of the developed countries compared to those that had smaller industrial bases.
At first, this seemed paradoxical. The developed countries had lower incidences of infectious diseases but showed a substantial and corresponding increase in allergic diseases such as asthma and hay fever. The “old friends hypothesis” was proposed as a reconciliation. This theory proposes that our evolutionary development has been dependent on critical associations with particular microbes.
In modern society, people are experiencing a reduced variety of microbial exposures, that, in turn, is affecting the normal development of our immune systems. The basic idea is that as we urbanize and sanitize, we are no longer associating with important microbes in the same way that we had in the past. It is this deficient exposure to an optimum range of microbes that is triggering an increase in allergies and also to other diseases linked to disordered immune systems, such as multiple sclerosis and Type I diabetes. The result is our recent epidemic increase in allergic diseases such as asthma, allergic rhinitis, or atopic dermatitis that has reached a point that one in five children are affected in some countries.
Numerous epidemiological studies have confirmed that children that grow up on farms are largely protected from asthma, hay fever, and a wide variety of allergic sensitizations. Contact with livestock and their feed from birth onward into adulthood seems to prevent the allergies and asthmatic reactions that afflict modern societies. A study that concentrated on inner-city urban environments found that the greater the amount of exposure in the first year of life to cockroaches, mouse droppings, cats, and their associated microbes, the lower the incidence of recurrent allergic wheezing and allergy symptoms.
Related Content: How to Optimize the Treatment of Asthma
We are not a single living thing
These new findings emphasize our deep relationship with the microbiome. In fact, it forces us to confront a changed understanding of our actual selves—we are much more than a single living thing. In fact, we are hologenomes, a combined life-form consisting of our own innate cells and an enormous array of co-existent and essential microbial life. Together, both our cells and our microbes collaborate to form the complex ecologies that form parts of our gut and other tissues.
Surprisingly, the number of microbes that are in us and on us outnumber our own personal cells by as many as 10 to 1. The total amount of their genetic material surpasses our own by 100 to 1. And these microbes are not just hanger’s on. Instead, they are crucial participants in our health, development, and well-being. They contribute to critical aspects of our metabolism, immune systems, and digestive health, as well as assist in the function of our nervous systems. They even influence our behaviors and moods. Our weight and appetites are partially dependent upon them.
Pet owners have long understood that their pets are affectionate companions and stress relievers. Now, they can take satisfaction in knowing that they are also a boon for not only their own sense of well-being and health, but also for their children’s microbiomes. It even extends outwards as a positive influence on the immune systems of other people’s children when they come into contact with their pets during that critical immunological period during pregnancy and the first months of life.
Bill Miller, MD
Dr. Bill Miller had been a physician in academic and private practice for over thirty years. He is the author of The Microcosm Within: Evolution and Extinction in the Hologenome. Dr. Miller is an internationally recognized evolutionary biologist and an expert on the emerging science of the microbiome. He is the author/co-author of numerous academic papers on the microbiome and evolution, serves as guest editor of a major academic biology journal and is co-editor of a forthcoming textbook on developmental and evolutionary biology.