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Chapter 5 : Epstein-Barr Virus
Epstein-Barr virus (EBV), a gamma herpesvirus, is a ubiquitous cause of infection in humans worldwide ( 1 ). Evidence of prior infection is present in adults throughout the world, with over 90% showing a serologic response. Exposure typically occurs early in life, with the majority of children in developing countries becoming seropositive by age 5. While onset of infection is delayed in areas with greater socioeconomic development, adults are almost uniformly positive. EBV is most commonly transmitted by contact with respiratory secretions, which promotes access and entry into the reticuloendothelial cells of the upper respiratory tree. While the primary target cell of EBV is the B lymphocyte, infection of a wider range of cell types can occur in immunocompromised hosts, particularly in those of epithelial lineage. Pharyngeal infection is followed by dissemination of virus throughout the body, with B lymphocytes as the primary target. The immune response to infection mounts steadily, with expansion of EBV-specific cytolytic T-cell clones eventually recognizing and controlling the primary infection. Control of EBV proliferation is signaled by a shift from lytic viral activity (marked by lytic proteins associated with cell destruction, such as BZLF1 and BRLF1) to a latent phenotype in an immortalized B lymphocyte pool, which provides a lifelong source of low-grade reactivation. Development of a serological response, with initial IgM and IgG to viral capsid antigen, followed by antibody to the EBV nuclear antigen developing months after infection, provides reliable markers for acute and chronic infection in immunocompetent hosts.