Common fungus may raise asthma risk

BOSTON — A fungus among us may tip the body toward developing asthma.

There’s mounting evidence that early exposure to microbes can protect against allergies and asthma (SN Online: 7/20/16). But “lo and behold, some fungi seem to put kids at risk for asthma,” microbiologist Brett Finlay said February 17 at a news conference during the annual meeting of the American Association for the Advancement of Science.

Infants whose guts harbored a particular kind of fungus — a yeast called Pichia — were more likely to develop asthma than babies whose guts didn’t have the fungus, Finlay reported. Studies in mice and people suggest that exposure to some fungi can both trigger and exacerbate asthma, but this is the first work linking asthma to a fungus in the gut microbiome of infants.

Finlay, of the University of British Columbia in Vancouver, and his colleagues had recently identified four gut bacteria in Canadian infants that seem to provide asthma protection. To see if infants elsewhere were similarly protected by such gut microbes, he decided to look at another population of children with an asthma rate similar to Canada’s (about 10 percent). He and his colleagues sampled the gut microbes of 100 infants in rural Ecuador and followed up five years later.

The researchers identified several factors that might influence risk of developing asthma, such as exposure to antibiotics, having respiratory infections, and whether or not the infants were breastfed. Of the 29 infants in the high-risk asthma group, more than 50 percent had asthma by age 5, Finlay said.

Surprisingly, the strongest predictor of whether a child developed asthma wasn’t bacterial. It was the presence of Pichia. And the yeast wasn’t protective; it tipped the scales toward asthma.

Finlay speculated that molecules made by the fungi interact with the infants’ developing immune systems in a way that somehow increases asthma risk. It isn’t clear how the infants’ guts acquire the fungus; some species of Pichia are found in soil, others in raw milk and cheese. Finlay and his colleagues are now going to look for the fungus in Canadian children’s gut microbes..

The researchers also looked at other gut microbe‒related factors that upped the Ecuadorean children’s asthma risk. Children with access to clean water had higher asthma rates, Finlay said. While drinking clean water helps people avoid several ills such as cholera, the link to asthma highlights how some dirt can be protective, he said. “We’ve cleaned up our world too much.”

This research underscores that caution should be used when generalizing about our intestinal flora. “What’s emerging is that it is very personalized,” gastroenterologist Eran Elinav of the Weizmann Institute of Science in Rehovot, Israel, said at the news conference. For example, evidence implicates some fungi in the development of inflammatory bowel disease, Elinav said, but it depends on the individual.