A German epidemiological study, published in the New England Journal of Medicine, confirms previous findings that children living on farms are significantly less likely to develop asthma than others. This study shows that the lower susceptibility of farm children to asthma can largely be accounted for by the fact that they are exposed to a greater variety of microorganisms than other children living in the same regions. While the physiological mechanisms underlying the effect remain to be uncovered, the investigators did identify several species that might be responsible for the reduction in asthma risk.

For the study, the researchers focused on the microbes present in domestic interiors. They collected household dust from bedrooms of the study participants, and analyzed the bacterial and fungal DNAs in the samples. The results showed that farm children must cope with a much greater range of microorganisms than children who live in other types of environment.

The researchers found that the bacteria and fungi seem to act as “guardians of health,” as the more diverse the microbial population present, the lower the risk of asthma. Exactly how the cells and spores achieve this is still unclear, but the researchers have a few possible explanations.

“One possibility is that a particular combination of microbial species stimulates the innate immune system and so prevents it from entering a state that promotes the development of asthma,” says Markus Ege, MD, from the Children’s Surgical Clinic in the Dr. Von Hauner Children’s Hospital at the University of Munich Medical Center.

Another model shows that continuous exposure to many different microorganisms makes it more difficult for the species that potentially induce asthma to become the dominant forms in the lower respiratory tract—similar to the what occurs in the gastrointestinal tract, where a balanced population of microbes is necessary for optimal organ function.

The researchers point out, however, that microbial diversity alone is not enough to prevent asthma. More likely, it takes a particular consortium of species to exert a protective effect.

“Within the large spectrum of organisms that we examined, there are some that may be of special interest,” says Ege. “Among these are certain species of bacilli and staphylococci—S.sciuri, for instance—as well as fungi of the genus Eurotium.”

Source: University of Munich