Infectious mononucleosis or mononucleosis is a viral illness caused most frequently by the Epstein-Barr Virus (EBV). EBV belongs to the Herpesvirus family of viruses and is responsible for the majority of mononucleosis (mono) cases. Cytomegalovirus (CMV) is responsible for causing about 8% of cases of mono and also a member of the Herpesvirus family. The characteristic set of symptoms for mono is the clinical triad of sore throat, fever and lymphadenopathy together with significant malaise. Physical examination reveals pharyngitis and lymphadenopathy, and laboratory analysis reveals atypical lymphocytosis, heterophile antibody, and evidence of mild hepatitis. Clinically, cases of mono caused by EBV are indistinguishable from those cases caused by CMV. Mono is most common in adolescents and young adults. EBV is efficiently transmitted from person to person via saliva, most commonly from sharing utensils and kissing. For this reason mono is sometimes referred to as "the kissing disease." EBV infects the majority of the population worldwide. Over 90% of adults worldwide are seropositive for EBV indicating that at some point they were infected with the virus.
EBV has a 2-5 week incubation period after which time the classic symptoms of acute mononucleosis appear. The clinical course of mono is strongly dependent on the age of the patient. Children often experience mild symptoms with primary EBV infection. In contrast, college age patients are generally more symptomatic. For most patients supportive care such as bed rest and hydration is the only therapy that is needed.
Although most patients experience a complete recovery from mono, there are several noteworthy complications. Autoimmune hemolytic anemia occurs in 0.5%-3% of infected patients. Mild thrombocytopenia (low platelet count) and mild neutropenia (low white blood cell count) may accompany mono infection. Enlargement of the spleen and subsequent splenic rupture is a rare, but potentially deadly complication. Due to this potentially deadly complication, patients with infectious mononucleosis should avoid contact sports.
Mononucleosis is diagnosed clinically based on the well-recognized mono-like symptoms. Tests for heterophile antibodies (e.g. antibodies to animal red blood cell antigens) can be detected to aid in the diagnosis.