A person with mononucleosis has a viral infection caused by Epstein-Barr virus or cytomegalovirus.

Symptoms include sore throat, fever, fatigue, rash, and gland swelling in the neck.

Mononucleosis is more common in college-age adults. Most people with this infection recover completely without treatment within 2 to 4 weeks. In some cases, the illness causes prolonged episodes of fatigue.