Pathophysiology
Clinical meaning
Hepatitis B virus (HBV) and hepatitis C virus (HCV) are blood-borne pathogens that cause inflammation and destruction of hepatocytes (liver cells), with significant potential for chronic infection and progressive liver disease. HBV is a partially double-stranded DNA virus of the Hepadnaviridae family. It enters hepatocytes by binding to the sodium taurocholate cotransporting polypeptide (NTCP) receptor on the cell surface. Once inside the cell, the viral DNA is transported to the nucleus where it forms covalently closed circular DNA (cccDNA) that serves as a template for viral replication. The immune-mediated destruction of infected hepatocytes, rather than direct viral cytotoxicity, causes the liver damage seen in hepatitis B. Cytotoxic T lymphocytes (CD8+ T cells) recognize viral antigens expressed on the surface of infected hepatocytes and destroy them. When the immune response is vigorous and coordinated, the infection is cleared (acute hepatitis with recovery). When the immune response is insufficient to clear the virus but strong enough to cause ongoing liver damage, chronic hepatitis develops. HBV transmission occurs through blood, sexual contact, and vertical (mother-to-child) transmission during birth. The chronicity rate is inversely...