text: Infectious mononucleosis (also known in North America as mono, the kissing disease, or Pfeiffer's disease, and more commonly known as glandular fever in other English-speaking countries) is a disease seen most commonly in adolescents and young adults, characterized by fever, sore throat, muscle soreness and fatigue (symptoms of a common cold or allergies). It is caused by the Epstein-Barr virus (EBV), which infects B cells (B-lymphocytes), producing a reactive lymphocytosis and the atypical T cells (T-lymphocytes).\n\nThe virus is typically transmitted from asymptomatic individuals through blood or saliva (hence "the kissing disease"), or by sharing a drink with friends/family, eating utensils, being coughed on, or being in close proximity of an infected person. The disease is far more contagious than is commonly thought. However, in rare cases a person may have a high tolerance to infection[citation needed].\n\nThe disease is so-named because the count of mononuclear leukocytes (white blood cells with a one-lobed nucleus) rises significantly. There are two main types of mononuclear leukocytes: monocytes and lymphocytes. They normally account for about 35% of all white blood cells. With infectious mononucleosis, it can become 50-70%. Also, the total white blood count may increase to 10000-20000 per cubic millimeter.