A virus previously considered harmless may trigger celiac disease in people predisposed to the condition. A report on the virus’s effects was published online today in the journal Science.

Experts estimate that celiac disease affects 1 in 133 people in the United States, although many of those people remain undiagnosed. (It's not the same thing as non-celiac wheat sensitivity.) When these people swallow something that contains gluten, their immune systems go haywire and begin attacking their own guts. This can cause not only abdominal pain, nausea, and bowel issues, but also difficulty absorbing nutrients. In kids, this could lead to stunted growth, weight loss, and delayed puberty.

Previous research found that celiac disease is genetic, in that a person is either genetically predisposed to get it or they aren’t. But most people with celiac-associated gene mutations don’t get celiac disease, and scientists didn’t know why.

One possibility is that the disease needs a jump-start—some sort of zap to the immune system. Ordinarily, reovirus would not be a candidate. It’s a common-enough pathogen, and doctors have long considered a reovirus infection to be harmless.

Researchers studying the virus began to suspect otherwise during a series of recent experiments on mice. The scientists had infected mice with two different strains of the virus. The mice given the first strain were fine, as was expected. Their immune systems switched on, but nothing went wrong.

The second strain was different. Mice who had been infected with this reovirus—one that commonly infects people, too—began getting sick when they consumed gluten. Their immune systems had switched on, then freaked out.

Senior author Bana Jabri of the University of Chicago said her team’s findings highlight the interconnectedness of pathogens, food triggers, and immunity.

“During the first year of life, the immune system is still maturing, so for a child with a particular genetic background, getting a particular virus at that time can leave a kind of scar that then has long-term consequences," Jabri said in a statement. "That's why we believe that once we have more studies, we may want to think about whether children at high risk of developing celiac disease should be vaccinated."