The Epstein–Barr virus (EBV), also called human herpesvirus type 4 (HHV-4), is a virus of the herpesviridae family. The virus occurs worldwide, and most people become infected with HHV-4 sometime during their lives. HHV-4 causes infectious mononucleosis and the symptoms are fever, sore throat, and swollen lymph glands. Sometmes, a swollen spleen or liver involvement may develop. Heart problems or involvement of the central nervous system occurs only rarely, and infectious mononucleosis is almost never fatal.