I copied this from americanpregnancy.org
What is Cytomegalovirus (CMV)?
Cytomegalovirus (CMV) is a virus that can be transmitted to a developing child before birth. CMV infection is usually harmless and rarely causes illness. For most healthy persons who acquire CMV after birth, there are few symptoms and no long-term health consequences. Once a person becomes infected, the virus remains alive, but usually dormant within that person’s body for life. There are two different types of infection: primary CMV and recurrent CMV infection. Primary infection can cause more serious problems in pregnancy than recurrent infection can. However, if a person's immune system is seriously weakened in any way, the virus can become active and cause CMV disease. For the majority of people who have CMV infection, it is not a serious problem.
I'm not totally sure. It's in the herpes family. But it sounds a lot like mononucleosis in that you get flu-like symptoms that eventually go away and it lives dormant in you for the rest of your life, but it can be dangerous to unborn babies.