U.S. researchers confirmed cytomegalovirus as a cause of the most common salivary gland cancers and it may be involved with more cancers. Lead author Michael Melnick of the Ostrow School of Dentistry at the University of Southern California and colleagues said designating cytomegalovirus as an oncovirus -- cancer-causing virus -- came after rigorous study of both human salivary gland tumors and salivary glands of postnatal mice. \"Cytomegalovirus is incredibly common; most of us likely carry it because of our exposure to it,\" Melnick said in a statement. \"In healthy patients with normal immune systems, it becomes dormant and resides inactive in the salivary glands. No one knows what reactivates it.\" The classification of cytomegalovirus as an oncovirus has important implications for human health, Melnick said. The virus, which has an extremely high prevalence in humans, can cause severe illness and death in patients with compromised immune systems, can cause birth defects if a woman is exposed to the virus for the first time while pregnant and it might be connected to other cancers besides salivary gland cancer, Melnick said. The study was published online in the journal Experimental and Molecular Pathology.