US researchers have come across a virus that may make us stupider—and it’s turning up in the throats of otherwise-healthy people, the Independent reports. Some 43% of 92 people in a study were found to have the virus. Those affected scored about 10% lower on tests involving visual processing, Science reports; for instance, it took them comparatively longer to draw a line through a numerical sequence on a page. Their attention spans also appeared to be shorter. “There’s more and more studies showing that microorganisms in your body have a bigger influence than anything anyone would have predicted, and this could be something along those lines,” says a researcher.