Infection by certain intestinal worms may help to foster the growth of bacteria that protect against gut inflammation.

Mutations in the NOD2 gene are linked to an inflammatory bowel disease called Crohn's. In mice lacking this gene, researchers discovered that introducing parasitic helminths to the gut helped to reverse cellular defects in the small intestine and reduce inflammation. Ken Cadwell at the New York University School of Medicine and his colleagues found that the worms promoted the growth of Clostridiales bacteria, which suppressed inflammation-causing Bacteroidales microbes in the gut. The researchers also observed a similar protective balance of intestinal microbes in people from rural areas (where helminth infections are relatively common), which was not seen in people from urban regions.

The results support the hygiene hypothesis, which says that a 'cleaner' microbial environment has made some people more susceptible to inflammatory disorders.

Science (2016)