The microbial environment and its influence on asthma prevention in early life

It’s a tale of two farming communities: one run by the Amish, who retain very traditional farming practices with horses for field work, and other run by Hutterites, who have embraced modern farming technologies.  Despite coming from the same genetic background and having otherwise similar lifestyles, the Hutterites have a greater than 40% rate of allergen sensitization, while the Amish have a rate lower than 7.5%.  What can account for such a difference?  As Dr. von Mutius outlines in this month’s issue of JACI, it’s likely in the billions of bacteria that colonize the skin, gut, and respiratory passages as well as those that live all over your house, workplace, and everywhere in between (J Allergy Clin Immunol 2016; 137(3): 680-689).

Believe it or not, it’s only been within the past few years that we’ve even found out about all these bacteria.  New technology has enabled scientists to take a closer look at the microbiome, the collection of microbes that colonize virtually everything around and within us.  These microbiomes are diverse and dynamic; and can provide fingerprints about the world around us.  Cat and dog ownership can be predicted by the presence of certain bacteria.  More significantly, the presence of certain bacteria, like H. influenzae, M. catarrhalis, and S. pneumoniae in the throats of 1 month old infants, and somewhat predict the development of persistent wheeze and asthma by age 6.

This is seen in larger epidemiologic studies.  Children who enter daycare before their first birthday are at much lower risk of developing allergen sensitization compared to those who enter after their second birthday.  And, as mentioned above, upbringing on a farm with animal husbandry, especially around dairy animals, confers significant protection.  This is extended to urban environments as well, where exposure to high levels of cockroach, mouse, and cat allergens in the presence of Firmicutes and Bacteroidetes bacteria actually conferred some protection against asthma.

This field is evolving tremendously, and there are still a lot of unanswered questions.  We still don’t know which particular microbes are protective and whether increased diversity really does help to prevent sensitization to allergens.  Nevertheless, with newer, more sensitive technologies that can scan and identify bacterial and other microbial DNA, we’re on the path towards better understanding how our microbial environment shapes our susceptibility to asthma, allergies, and other immune disorders.