Hepatitis D Introduction and Definitions

Delta hepatitis was first recognised following the detection of a novel protein, termed delta antigen, by immunof-luorescent staining in the nuclei of liver cells in biopsy specimens from patients with chronic active hepatitis B. Later this antigen was found to be a component of a new RNA virus enveloped by the surface antigen of HBV. Hepatitis delta virus (HDV) requires a helper function of HBV for its transmission.

Two forms of delta hepatitis infection are known. In the first, a susceptible individual is coinfected with HBV and HDV, often leading to a more severe form of acute hepatitis caused by HBV. In the second, an individual infected chronically with HBV becomes superinfected with HDV. This may cause a second episode of clinical hepatitis and accelerate the course of the chronic liver disease, or cause overt disease in asymptomatic carriers of hepatitis B. HDV is cytopathic and HDAg may be directly cytotoxic.

Delta hepatitis is common in the Mediterranean region, parts of eastern Europe, the Middle East, Africa, South America and some islands in the South Pacific region. It has been estimated that 5% of hepatitis B carriers worldwide (approximately 18 million people) are infected with HDV. In areas of low prevalence of HBV, those at high risk of hepatitis B, particularly intravenous drug abusers, are also at risk of HDV infection.

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