German scientists have identified bacteria in cows’ digestive systems and manure that may help children avoid developing asthma. The catch: They have to inhale the germs.
As allergies, asthma, eczema and hay fever rose in industrial societies, children raised on farms seemed to be spared. By the 1990s, research suggested that certain childhood infections helped train the immune system instead of leaving it to overreact to dust, pollen and other allergens. The idea became known as the “hygiene hypothesis” — that staying too clean carried a cost.
Researchers at Ludwig Maximilian University Hospital and the Institute of Asthma and Allergy Prevention at Helmholtz Munich in Germany measured the bacteria children inhale while playing or working in cow barns and traced the mechanism that helps reduce lung inflammation.
“Girls and boys who grow up on farms and are exposed to a wider variety of microbes have the problem far less often,” epidemiologist Markus Ege said in a news release. “With our new study, we can make a much stronger case, because we can identify the individual links in the proposed causal chain: the bacteria, the relevant microbial metabolic products, and the human receptors.”
The team analyzed data from more than 1,000 children in European rural health studies. It compared nasal swabs, mattress dust and airborne samples from cowsheds collected from 47 farm children. The findings were published July 28 in the New England Journal of Medicine.
In the microbial mix of the farm environment, the study identified nine gram-positive environmental bacterial genera. Together, they explained two-thirds of the link between farm exposure and lower asthma rates. The findings ruled out fungus as a factor.
Those bacteria produced chemicals that appear to switch on proteins in the human body that help control the immune system and inflammation. The compounds include kynurenine and xanthine, which activate a protein called the aryl hydrocarbon receptor, and alpha-linolenic acid and stearidonic acid, two fatty acids that activate another protein called PPAR-gamma. Both receptors are common in human airway cells.
The researchers wrote that high levels of stimulation were detrimental, while moderate levels — indicating only brief time spent in cowsheds — seemed to be beneficial.
The effect of cow bacteria does not benefit everyone. Small genetic variations, especially in genes involved in sensing molecules produced in the body or influenced by the gut microbiome, could affect the results.
The effect is common enough, Ege said, to suggest new medical treatments to prevent asthma in children who do not have access to cowsheds.
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