Intestinal worms manipulate their host's immune system to ensure their survival, in part by changing the metabolism of the host's gut microbiome.

The worms, called helminths, infect around 2 billion people around the world, and are able to block harmful inflammatory responses in humans and mice. Nicola Harris at the Swiss Federal Institute of Technology in Lausanne and her colleagues studied mice infected with the helminth Heligmosomoides polygyrus bakeri, and found that mice that had been treated with antibiotics to kill gut bacteria before being exposed to the worms had more allergic airway inflammation than did untreated, worm-infected animals. Worm infection caused the microbiota to produce increased levels of short-chain fatty acids in mice, pigs and six out of eight human volunteers. The anti-inflammatory effects of worm infection were lost in mice that had been engineered to lack a receptor for the fatty acids.

The findings suggest that helminths and gut microbes have evolved this mechanism to regulate the host immune system over many millions of years, the authors say.

Immunity http://dx.doi.org/10.1016/j.immuni.2015.09.012 (2015)