Medical Matters: How farm dust and gut bugs can fight allergens

The prevalence of allergies has increased hugely in the past 20 years. In the developed, industrial world it is estimated that up to half of children have at least one allergy: most commonly, skin problems such as eczema, respiratory allergens such as asthma and rhinitis. Food allergies are also on the rise.

Readers of a certain vintage will recall a more innocent era when children living in urban areas were free to roam in nearby fields and waste ground. In the process, they and their country cousins came into contact with a broad range of microbes. In most cases, these did not cause illness but nonetheless stimulated a mild immune system response. It seems this resulted in a natural maturation of our immune systems, which made them less likely to react inappropriately to food and dust, resulting in a lower prevalence of allergies.

According to Dr Avery August, professor of immunology at Cornell University, children who grow up on farms have a wider diversity of microbes in their gut, and have up to 70 per cent reduced prevalence of allergies and asthma compared with children who do not grow up on farms.

And a new study from Belgium is one of the first to establish a causal relationship between farm life and allergy resistance. The research, into some 2,000 children, found that a specific protein called A20 is the reason children living on farms enjoy increased resistance to allergies. A20 is a protective protein in the mucous membrane of the lungs that reduces the body’s response to allergens.

Farm dust

Breathing in farm dust, Belgian researchers write in the journal Science, causes the lungs to produce more A20. This, in turn, reduces allergic reactions to other kinds of dust. It seems this process occurs when the lungs are still developing early in a child's life.

Meanwhile, Canadian researchers have just identified four specific bacteria that appear to protect children from developing asthma if they are exposed to the microbes before the age of three months.The four types of bacteria were Faecalibacterium, Lachnospira, Veillonella and Rothia, which the scientists from the University of British Columbia nicknamed FLVR. Of the children in the small study, 22 were considered at very high risk of developing asthma because they showed early warning signs, such as wheezing. At three months, all of them showed low levels of the FLVR bacteria in faecal samples; so far eight have been diagnosed with asthma.

But August points to the potential for something of a perfect storm in the allergy story, with research suggesting a link between antibiotic overuse and the development of allergies. While antibiotics fight infection, they also reduce the normal bacteria in our gastrointestinal system, the so-called gut microbiome.

“Because of the interplay between gut bacteria and the normal equilibrium of cells of the immune system, the gut microbiome plays an important role in the maturation of the immune response,” he writes. “When this interaction between bacteria and immune cells does not happen, the immune system responds inappropriately to innocuous substances such as food or components of dust.”

Antibiotics and infants

A 2005 study found that infants exposed to antibiotics in the first four to six months have a 1.3- to 5-fold higher risk of developing an allergy. Infants with reduced bacterial diversity, which can occur with antibiotic use, have an increased risk of developing eczema. Their mothers may also be part of the equation: a large Danish study on asthma in childhood found that children whose mothers took antibiotics during pregnancy were almost twice as likely to develop asthma compared with children whose mothers did not take antibiotics when pregnant.

This all sounds like another compelling argument for patients to stop pressurising doctors for antibiotics for colds and sore throats, and for medics to stop overprescribing a precious tool in the fight against serious infection.

mhouston@irishtimes.com muirishouston.com