Cytomegalovirus (CMV) is one of the herpesviruses. CMV is a common infection that is usually harmless. Once CMV is in a person’s body, it stays there for life. Most healthy children and adults infected with CMV have no symptoms and may not even know that they have been infected. Others may develop a mild illness when they get infected and have the following symptoms: sore throat, fever, fatigue, and swollen glands. CMV can also cause serious disease in babies who were infected with CMV before birth.