Chronic, active Epstein-Barr virus infection is a serious disorder that is distinguished by the presence of constant illness after a period of greater than six months, from the time of an initial mononucleosis diagnosis, explains Mayo Clinic. In medical terms, chronic is defined as three months or more, notes MedicineNet.
Mononucleosis is usually caused by being infected with the Epstein-Barr virus or EBV. Symptoms of mononucleosis include weakness, sore throat, fever and swollen lymph nodes, states Mayo Clinic.
A person carries the Epstein-Barr virus for life once infected with it, notes Mayo Clinic. Though usually dormant, the virus can reactivate, but does not typically cause illness. People whose immune systems are weak can become ill with the reactivation of the Epstein-Barr virus.