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mononucleosis mon·o·nu·cle·o·sis (mŏn'ō-nōō'klē-ō'sĭs, -nyōō-)
Abnormally large numbers of mononuclear white blood cells in the blood, especially forms that are not normal.
An acute and infectious disease caused by a virus; its symptoms include fever, swelling of the lymph nodes, and general exhaustion. Mononucleosis gets its name from the kind of white blood cell (monocyte) that increases in number in the blood of persons who have the disease. There is no specific treatment, but sufferers usually recover within a few weeks.
Note: Mononucleosis is sometimes called the “kissing disease,” because at one time the virus was thought to be transmitted by kissing. The virus can be found in the saliva of those who have the disease, so there may be some truth in the belief.