Most people who have infectious mononucleosis, or mono, get it only once. Rarely, however, mononucleosis symptoms may recur months or even years later.Most cases of mononucleosis are caused by infection with the Epstein-Barr virus (EBV). Once you're infected with EBV, you carry the virus â usually in a dormant state â for the rest of your life. Periodically, however, the virus may reactivate. When this happens, the virus can be detected in your saliva â but you're not likely to become ...