Is Idiopathic Pulmonary Fibrosis Caused by a Virus? The cause(s) of idiopathic pulmonary fibrosis have vexed researchers for decades. Although risk factors (smoking, familial gene mutations) provide clues, the actual trigger for the proliferative, fibrotic cellular process resulting in usual interstitial pneumonitis (on biopsy specimens) and IPF (clinically) have remained frustratingly elusive. But an exciting new case-control study suggests that in at least some people, idiopathic pulmonary fibrosis may be caused by a virus called herpesvirus saimiri. Virginia Folcik, Gerard Nuovo