simon phipps , qimr berghofer medical research institute and md. al amin sikder , the university of queensland
given asthma is about five times more common in western societies, this suggests lifestyle plays a major role. and as it usually develops in childhood, many studies have attempted to look at the events that transpired in infants who did or did not develop asthma by school age.
a common finding in those who developed asthma is that they had experienced a severe respiratory viral infection or “viral bronchiolitis” in early life. other studies have shown respiratory viruses trigger asthma exacerbations or “attacks” in those who already have asthma. so in already susceptible individuals, respiratory virus infections contribute to the onset, progression, and exacerbations of asthma.
our immune system has a number of mechanisms to fight viruses. one of these is the production of proteins called interferons – so called because they interfere with viral replication. in some studies , cells from patients with asthma produced lower levels of interferons, suggesting this may make someone more susceptible to a respiratory virus, and then asthma.
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several new therapies involving antibodies that neutralise or absorb these proteins are now entering the market. some are available now, including one called “ anti-interleukin-5 ”.
we don’t know quite as much about the less dominant forms of asthma, but inroads are being made in this area too. one recent landmark study , for example, reported that including azithromycin (an antibiotic) as an add-on therapy reduced the number of exacerbations in patients with eosinophilic asthma, but also those with non-eosinophilic asthma.
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in the late 80s an observation was put forward that younger siblings in large families have a lower risk of developing allergies, and this could be because they were exposed to more germs. this was known as the “ hygiene hypothesis ”.
the hygeine hypothesis is now thought to be more of a “microbiota hypothesis” as the microbiota assembles and matures in early life. recent studies show infants who are at high risk of developing asthma have an imbalanced gut microbiota at one month of age.
the composition of the microbiota can change rapidly (within days), contains 150 times more genes than our genome, and is heavily influenced by our mother’s microbiota, particularly in early-life. this is now placing the spotlight on western lifestyle choices , and how these influence the metagenome (which is our genome together with the multitude of microbial genomes).
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a number of elegant studies , largely performed in animal models, have demonstrated that diet affects the composition of the gut microbiota, which in turn, affects gut health but also all other organs and tissues.
a study found treatment of mice with antibiotics (which disturb the microbiota) diminishes their ability to produce interferon proteins in response to influenza virus infection.
and a recent study showed poor maternal diet in the third trimester of pregnancy increases the severity of viral bronchiolitis in the offspring. the investigators of this large study didn’t explore whether this effect was associated with alterations to the microbiota, which is the likely explanation, and this is something we need to find out.
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once we know more about the link between asthma and the bugs that reside within and on us, we’ll be better able to treat and hopefully prevent asthma.
this article is republished from the conversation under a creative commons license. read the original article .