Children who grow up on farms have a lower risk of developing asthma, and now research published in Nature Medicine, DOI: 10.1038/s41591-019-0469-4 shows that may be due to microbes that can also be found in urban and suburban homes.
Pirkka Kirjavainen at the National Institute for Health and Welfare in Finland and his colleagues analysed the microbes from living room floor dust from the homes of a group of 197 children living in rural areas of Finland – half living on farms – and 182 children living in suburban or urban places.
They took these samples when the children were 2 months old and likely to be crawling, and therefore exposed to microbes on the floor. Then they followed up at 6 years old to see how many children were diagnosed with asthma.
For the rural group there was a clear difference in the dust found in farms compared to other homes. The dust from farm homes had a high variety of bacteria, including those from cattle that were not present in non-farm homes. Non-farm homes had a higher proportion of human-associated bacteria, including members of the Streptococcaceae family and Straphylococcus genus.
These differences were associated with differences in asthma rates, with asthma being rarest among children brought up on farms. About 19 per cent of the children on non-farm homes had asthma, while only 9 per cent of kids on farms did. “Where there are more outdoor microbes and a low abundance of human microbes, we see lower asthma rates,” says Kirjavainen.
For the suburban children, they found that the homes with a microbial community that was most like that of farm homes were correlated with a lower risk of asthma in the children at age 6, when asthma tends to develop.
“There is an indication that early life exposure matters the most. Later exposure would seem to have an influence on asthma, but this is the optimal window to measure,” says Kirjavainen.
When the team studied blood samples from the children, they found that those in homes with more farm-like bacteria didn’t produce immune responses to the bacteria, so they tolerate them better. The team then replicated this study with a group of 1031 German children, and found the same relationship between farm-like microbes in non-farm homes and a reduced risk of childhood asthma.
Kirjavainen says there was a small association between having pets and farm-like microbes in the home, which could be due to the animals bringing in soil particles. The team saw no effect when they took into account gender, parental allergies, maternal education, smoking during pregnancy, or the number of siblings a child had. The next step is to determine what it is about the microbes that make them beneficial, and potentially devise a therapy that could induce these immune system effects in children.