Clinical meaning
Epstein-Barr virus (EBV), also known as human herpesvirus 4 (HHV-4), is a member of the Herpesviridae family and is one of the most common human viruses worldwide, infecting approximately 95 percent of the adult population globally. EBV has a particular tropism for B lymphocytes and oropharyngeal epithelial cells. Primary infection typically occurs during childhood (often subclinical) or adolescence/young adulthood, when it commonly manifests as infectious mononucleosis (IM), colloquially known as the 'kissing disease.' The virus is transmitted primarily through saliva (oral secretions), making kissing, sharing utensils, and sharing drinking containers the most common modes of transmission. After primary infection, EBV establishes lifelong latency in memory B lymphocytes, with periodic reactivation and asymptomatic viral shedding in saliva. The pathophysiology of infectious mononucleosis involves EBV infection of B lymphocytes in the oropharyngeal lymphoid tissue (Waldeyer ring). The virus stimulates polyclonal B cell proliferation, which triggers a robust cytotoxic T lymphocyte (CD8+) response. These activated T lymphocytes are the 'atypical lymphocytes' (Downey cells) seen on the peripheral blood smear, which is a hallmark laboratory finding of infectious mononucleosis. The intense immune response causes...