Cytomegalovirus is a large herpes-type virus commonly found in humans that can cause serious infections in people with impaired immunity. The infection may result in pneumonia, gastroenteritis, retinitis or encephalitis. Antiviral medications may stop the replication of the virus but will not destroy it. Update Date: 11/01/2007Kenneth M. Wener, M.D., Department of Infectious Diseases, Lahey Clinic, Burlington, MA. Review provided by VeriMed Healthcare Network.