Infectious Mononucleosis (Mono) By Kenneth M Kaye, MD, Harvard Medical School Reviewed / Revised Sep 2021 | Modified Sep 2022 View Patient Education Pathophysiology Symptoms and Signs Diagnosis Prognosis Treatment Key Points Topic Resources Infectious Mononucleosis... Infectious Mononucleosis... Infectious mononucleosis is caused by Epstein-Barr virus (EBV, human herpesvirus type 4) and is characterized by fatigue, fever, pharyngitis, and lymphadenopathy.