Cytomegalovirus is a virus in the herpes family that can cause infections in people with compromised immune systems. Most adults have been infected with cytomegalovirus at some time in their lives -- many in childhood, and some even before birth.
Upon infection, cytomegalovirus can cause symptoms such as fatigue, weakness, prolonged fever, swollen glands, sore throat, and achy muscles or joints. Symptoms are usually short-lived, and then the virus remains dormant in your body.
Cytomegalovirus can become active again if you have an illness or are taking medications that suppress the immune system. Some researchers believe that cytomegalovirus plays a role in chronic fatigue syndrome, but this link is not proven.