Dogs, Bacteria, Microbiomes and Asthma

PigPen does not have allergies

The 112th General Meeting of the American Society for Microbiology was held last week in San Francisco, and among the many papers presented was one about dogs, microbiomes and asthma.

By the late 90s it had become evident that the prevalence of allergic diseases and asthma was on the rise in urban populations of developed countries and one of the links found was the relationship between childhood exposure to farm animals and a reduction in the prevalence of allergies and asthma.[1] Analysis of the dust from houses in farms found significantly higher levels endotoxins when compared to rural but non-farm houses.[2]

Around the same time two studies from Norway and Sweden would report that childhood exposure to pets was “associated with a lower prevalence of allergic rhinitis and asthma” [3] and that “early-life exposure to pets or lifestyle factors associated with exposure to pets reduce the risk of developing atopy-related diseases in early childhood.” [4]

The same story has been repeated in various forms, like the 2006 paper [4] that found a decrease in infant wheezing in homes with dogs and high levels of endotoxins.

Lab Mouse with KimWipes

That’s a bit of background. I don’t have anything much to add to the press release and since it’s well written I won’t even summarize it. Microbiome research has over the last few years become a hot topic, due to the ease and low cost of genetic analysis and the realization of the complex role they play in our bodies.  The hope is that future research can provide greater insight into how our bodies interact with our microbial guests and the effects on our health. This fervor has also fueled major projects like the Human Microbiome Project and the Earth Microbiome Project.

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The ASM Press Release

Dog-Associated House Dust Protects Against Respiratory Infection Linked to Asthma

SAN FRANCISCO — June 19, 2012 — House dust from homes with dogs appears to protect against infection with a common respiratory virus that is associated with the development of asthma in children.  Researchers from the University of California, San Francisco, present their findings today at the 2012 General Meeting of the American Society for Microbiology.

“In this study we found that feeding mice house dust from homes that have dogs present protected them against a childhood airway infectious agent, respiratory syncytial virus (RSV).  RSV infection is common in infants and can manifest as mild to severe respiratory symptoms.  Severe infection in infancy is associated with a higher risk of developing childhood asthma,” says Kei Fujimura, a researcher on the study.

In the study Fujimura and her colleagues compared three groups of animals:  Mice fed house dust from homes with dogs before being infected with RSV, mice infected with RSV without exposure to dust and a control group of mice not infected with RSV.

“Mice fed dust did not exhibit symptoms associated with RSV-mediated airway infection, such as inflammation and mucus production.  They also possessed a distinct gastrointestinal bacterial composition compared to animals not fed dust,” says Fujimura.

Pet ownership, in particular dogs, has previously been associated with protection against childhood asthma development, says Fujimura.  Recently she and her colleagues demonstrated that the collection of bacterial communities (the microbiome) in house dust from homes that possess a cat or dog is compositionally distinct from house dust from homes with no pets.

“This led us to speculate that microbes within dog-associated house dust may colonize the gastrointestinal tract, modulate immune responses and protect the host against the asthmagenic pathogen RSV,” says Fujimura.  “This study represents the first step towards determining the identity of the microbial species which confer protection against this respiratory pathogen.”

Identification of the specific species and mechanisms underlying this protective effect represents a crucial step towards understanding the critical role of microbes in defining allergic disease outcomes and could lead to development of microbial-based therapies to protect against RSV and ultimately reduce the risk of childhood asthma development, says Fujimura.

This work represents a collaboration between the Lynch lab at University of California San Francisco and the Lukacs lab at the University of Michigan, Ann Arbor. Tine Demoor, a post-doc in Nick Lukacs lab, performed the mouse experiments and measured airway symptomology associated with RSV infection. Fujimura,  Marcus Rauch, and Stephanie Galang from Susan Lynch’s group performed microbiome profiling and data analysis of cecal (gut) contents from these animals.

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I guess I finally have good excuse as to why I let my childhood dog sleep on my bed no matter how dirty he got …..maybe Mom will finally buy it.

REFERENCES

1.  Riedler J, Eder W, Oberfeld G, Schreuer M: Austrian children living on a farm have less hay fever, asthma and allergic sensitization. Clin Exp Allergy 2000, 30:194–200.

2.   Von Mutius E, Braun-Fahrlander C, Schierl R, Riedler J, Ehlermann S, Maisch S, Waser M, Nowak D: Exposure to endotoxin or other bacterial components might protect against the development of atopy. Clin Exp Allergy 2000, 30:1230–1234.

3. Hesselmar Åberg, Åberg, Eriksson and Björkstén. Does early exposure to cat or dog protect against later allergy development? Clinical & Experimental Allergy, 29: 611–617. doi: 10.1046/j.1365-2222.1999.00534.x

4. Nafstad P, Magnus P, Gaarder P I , Jaakkola1 J J K. Exposure to pets and atopy-related diseases in the First 4 years of life.  Allergy 2001: 56: 307-312

5. Campo P, Harpinder K K, Levin L, Reponen T, Olds R. Influence of dog ownership and high endotoxin on wheezing and atopy during infancy. J Allergy Clin Immunol. 2006 December ; 118(6): 1271–1278.

RELATED LINKS

The International Human Microbiome Consortium

Respiratory Syncytial Virus Infection (RSV)

Atopy – Wikipedia