Abstract
The five hepatotropic viruses, hepatitis A virus (HAV), hepatitis B virus (HBV), hepatitis C virus (HCV), hepatitis delta virus (HDV), and hepatitis E virus (HEV), are implicated in most cases of acute viral hepatitis. HAV and HEV are enterically transmitted, HDV and HCV are spread predominantly through parenteral exposure; HBV is also spread parenterally, through intimate contact, and by vertical transfer from mother to infant. Hepatitis viruses have a global distribution, HAV and HEV are endemic in most developing countries and HBV is highly endemic in sub-Saharan Africa and Asia. As hepatitis viruses are largely noncytopathic, liver damage in acute (and chronic) hepatitis reflects host immune responses, largely controlled by CD4 T-helper lymphocytes, directed at viral- or self-antigens expressed on the surface of infected hepatocytes via the major histocompatibility complex (MHC). Acute viral hepatitis characteristically presents with systemic complaints such as malaise and jaundice, and generally cannot be distinguished by clinical or biochemical features. HBV, HDV, and HCV also cause chronic hepatitis, with the risk of progression to cirrhosis and hepatocellular carcinoma. Effective vaccines are available for HAV and HBV. Although achieving viral eradication in chronic HBV and HCV with current therapies is not universal, newer antiviral drugs are promising.