The Epstein–Barr virus (EBV) is a tumourogenic herpes virus that has been implicated in a wide range of human illnesses such as Hodgkin's disease and B lymphoproliferative disease; however it most commonly causes infectious mononucleosis (IM) often referred to as glandular fever (Macsween & Crawford, 2003). Primary infection with EBV typically occurs subclinically between the ages of one and six, after which the virus latently inhabits B lymphocyte cells. Previous infection with EBV is indicated by the presence of EBV antibody titres in the serum, while lack of these antibodies indicates vulnerability to EBV infection (Kasl et al., 1979). In the Western world, a second peak of EBV infection occurs between 14 and 20 years of age. Estimates suggest that 90% of the world's population are seropositive for EBV by the age of 30 and carry the virus as a lifelong latent infection (Papesch and Watkins, 2001).

Epstein–Barr virus and infectious mononucleosis

When people get infected with EBV, a number seroconvert without developing the clinical signs of IM. Those who develop the clinical syndrome experience an acute illness characterized by fatigue, sore throat, tender lymph nodes and fever, which usually resolves within two to four weeks (Rea et al., 2001). The puzzle is why some infected individuals develop clinical IM while others do not.

In an attempt to answer this question, Kasl and colleagues (1979) investigated 432 young American cadets over a four-year period.