Infectious Mononucleosis - Definition
Infectious mononucleosis (pronounced MON-o-NOO-klee-O-siss) is a contagious (catching) illness caused by the Epstein-Barr virus (EBV). The virus most commonly infects the liver, lymph nodes, and mouth. Mononucleosis is usually not a serious disease. However, its major symptoms—fatigue and lack of energy—can linger for several months. Infectious mononucleosis is also known as "mono" or "the kissing disease."

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