Mononucleosis (also called 'Mono', glandular fever, and, colloquially, the 'kissing disease'), is a disease most commonly caused by the Epstein-Barr virus (EBV). EBV affects the lymphocytes which are white blood cells involved in the adaptive immune system. Mononucleosis can also be caused by cytomegalovirus (HCMV), a herpes virus most commonly found in body fluids. While CMV can cause mononucleosis, 85% of the cases are associated with EBV. The disease can be found in anyone but is most commonly contracted by adolescents and young adults ages 1535. Mononucleosis is associated with fatigue that can last up to several months. Symptoms are not usually felt until 47 weeks after exposure to EBV. While the disease is rarely fatal, occasionally the disease stays in the blood cells, affecting the person for the rest of his or her life. In every case, the person excretes the disease intermittently in saliva throughout their lives.