Question
Ebstein-Barr virus.
Answer
Epstein-Barr virus (EBV) is a member of the human herpesvirus family (HHV-4), a double-stranded DNA virus, transmitted primarily via saliva, that establishes lifelong latent infection in host B lymphocytes after the acute illness resolves.
Primary infection: causes infectious mononucleosis — fever, exudative pharyngitis, lymphadenopathy (typically posterior cervical), and splenomegaly, with atypical (reactive) lymphocytosis on peripheral smear (activated CD8+ cytotoxic T cells responding to EBV-infected B cells, rather than the infected B cells themselves).
Pathogenesis: EBV infects oropharyngeal epithelial cells and, via the CD21 receptor, B lymphocytes; infected B cells proliferate (polyclonal B-cell activation), and the vigorous cytotoxic T-cell response against these infected cells produces the characteristic atypical lymphocytosis; the virus then establishes lifelong latency in memory B cells, with periodic asymptomatic reactivation and shedding in saliva.
Laboratory diagnosis:
- Heterophile antibody test (Paul-Bunnell/Monospot test) — detects non-specific antibodies agglutinating sheep/horse RBCs; rapid screening test, though can be falsely negative early in illness or in young children.
- EBV-specific serology — IgM against viral capsid antigen (VCA-IgM) indicates acute infection; IgG against VCA and EBNA (Epstein-Barr nuclear antigen) indicates past infection.
- Peripheral blood smear — atypical lymphocytosis.
Associated malignancies: EBV is causally linked to several malignancies, reflecting its capacity to immortalize/transform infected B cells and, in some contexts, epithelial cells: Burkitt lymphoma (endemic African form, associated with a characteristic c-myc translocation), nasopharyngeal carcinoma (particularly in Southeast Asia), certain Hodgkin lymphomas, and post-transplant lymphoproliferative disease in immunosuppressed transplant recipients (where loss of normal T-cell surveillance allows EBV-driven B-cell proliferation to progress unchecked).
Complications of primary infection: splenic rupture (advise against contact sports during acute illness), upper airway obstruction from marked tonsillar/adenoidal enlargement, and a characteristic maculopapular rash if ampicillin/amoxicillin is inadvertently given for presumed bacterial pharyngitis.