Hepatitis

Hepatitis is an inflammatory condition of the liver most commonly caused by hepatotropic viruses (A–E), though non-infectious causes such as alcohol and drugs also exist.

Hepatitis A

Hepatitis A virus (HAV) is a non-enveloped RNA virus of the Picornaviridae family. It is primarily transmitted via the fecal-oral route, typically through ingestion of contaminated food or water. After ingestion, HAV enters the bloodstream through the oropharynx or intestinal epithelium and reaches the liver. The virus targets hepatocytes, replicating in the cytoplasm without causing direct cytopathic effects. Liver injury is instead mediated by the host immune response, particularly CD8+ T cells and natural killer (NK) cells. The disease is self-limiting, and chronic infection does not occur.

Hepatitis B

Hepatitis B virus (HBV) is a partially double-stranded DNA virus from the Hepadnaviridae family. Transmission occurs via blood, sexual contact, or perinatally. The virus enters hepatocytes via the sodium taurocholate co-transporting polypeptide (NTCP) receptor. Following entry, the relaxed circular DNA (rcDNA) is transported to the nucleus and converted into covalently closed circular DNA (cccDNA), which serves as a stable template for transcription. Viral mRNAs are exported to the cytoplasm, where viral proteins and pre-genomic RNA are synthesized. Assembly occurs in the cytoplasm, followed by reverse transcription of pre-genomic RNA into DNA within the nucleocapsid. New virions are released via the endoplasmic reticulum and Golgi apparatus. The persistence of cccDNA underlies chronic infection.

Hepatitis C

Hepatitis C virus (HCV) is an enveloped RNA virus in the Flaviviridae family. It is mainly transmitted through blood exposure. HCV binds to multiple receptors, including CD81 and claudin-1, to enter hepatocytes. Replication occurs entirely in the cytoplasm, where the viral RNA is translated into a single polyprotein, later cleaved into structural and nonstructural proteins. HCV evades the immune system through high genetic variability, contributing to chronic infection in over half of infected individuals.

While supportive care is the mainstay for HAV, chronic HBV and HCV infections require antiviral therapies to suppress viral replication and prevent complications such as cirrhosis and hepatocellular carcinoma.