Norovirus inflames the stomach and/or intestines and causes pain, nausea, vomiting, and diarrhea. It is super contagious and kills tens of thousands of people each year. But until now, we did not even know which cells it targets to create all this havoc. A recent study by a public-private consortium working in universities and Genetech has just discovered the elusive cell type (in mice): they’re called tuft cells, and they reside in the ilium and colon.

Obviously, norovirus attacks intestinal epithelial cells, the specialized cells that line tubes within the body. But last year, the same group reported that noroviruses would infect only a rare subset of them and not most of their neighbors. But the researchers could not discern what made these select cells so special.

They knew that norovirus used a particular receptor to infect cells and that this receptor is both necessary and sufficient for infection. Oddly, the receptor is an immunoregulator thought to be expressed by blood-forming cells, specifically immune progenitor cells in the bone marrow. These could make their way to the intestines once they mature. But mice that got bone marrow transplants that lacked this receptor were still susceptible to norovirus infection, so that’s clearly not the case.