[Hepatitis viruses]

Five different hepatitis viruses that cause acute and chronic hepatitis in human beings have been identified. Hepatitis viruses are designated by the letters A, B, C, D and E and abbreviated as HAV, HBV, HCV, HDV, and HEV, respectively. Although each belongs to a distinctly different virologic group, they share the feature of hepatotropism, which remains poorly understood. HAV and HEV are transmitted through a fecal-oral route. HDV, also referred to as the delta agent, is a defective, parenterally transmitted virus that uses the hepatitis B surface antigen (HBsAg) of HBV as its envelope. Thus, HDV infection occurs only in patient with HBV infection. Application of molecular biologic techniques has been instrumental in elucidating the genomic sequences of the individual hepatitis viruses and in understanding viral gene expression and mechanisms of viral replication. Knowledge of the genomic structure of these viruses and perfection of molecular biological techniques have also led to clinical applicability of molecular diagnostic techniques. Indeed, these molecular diagnostic techniques have rapidly become the standards against which serologic tests are compared.