Infectious mononucleosis is an acute infectious disease with fever caused by Epstein-Barr virus (EBV). The syndrome includes pharyngitis, lymphadenopathy and splenomegaly as well as leukocytosis due to atypical mononuclear cells. Young adults are most often afflicted. The fact that the virus is transmitted by saliva also gave it the name "Kissing Disease".
The incubation period is not precisely known, but may be up to 5-8 weeks. Fever, pharyngitis and symmetrical lymphadenopathy occur after a prodromal phase. Splenomegaly is usually present. Occasionally, severe cases with encephalitis occur. The symptoms normally resolve after 1-3 weeks. If amoxicillin is prescribed for treatment of the pharyngitis, a maculopapular exanthem will form. The diagnosis can be established using serological tests (anti-EBV IgM+) and EBV-PCR.
In general, a leukocytosis of 12-18 x 109/L exists. The leukocyte count can be either normal or decreased. The increased leukocytes are due to atypical mononuclear cells. Cytotoxic T lymphocytes are of concern here. They are classified morphologically as reactive atypical lymphocytes. Thrombocytopenia can occur. Anemia is rare and normally hemolytic in origin.
Similar blood picture abnormalities also occur in cytomegalovirus infection, toxoplasmosis and acute HIV infection.