Pathophysiology
Infectious mononucleosis occurs with infection by the Epstein–Barr virus.
The infection is spread via saliva, and has an incubation period of four to seven weeks. Symptoms usually persist for two to three weeks, but fatigue is often more prolonged.
The length of time that an individual remains contagious is unclear, but may be the highest during the first six weeks following infection. Some studies indicate that a person can spread the infection for many months after symptoms are completely gone, with one particular study indicating as long as 18 months.
The virus replicates first within epithelial cells in the pharynx (which causes pharyngitis, or sore throat), and later primarily within B cells (which are invaded via their CD21). The host immune response involves cytotoxic (CD8-positive) T cells against infected B lymphocytes, resulting in enlarged, atypical lymphocytes (Downey cells).
When the infection is acute (recent onset, instead of chronic), heterophile antibodies are produced.
Similar symptoms can be caused by cytomegalovirus, adenovirus, and Toxoplasma gondii, but will result in a negative heterophile antibody test.
Read more about this topic: Infectious Mononucleosis