HBV

The hepatitis B virus (HBV) is a small DNA virus with unusual features similar to retroviruses. HBV is classified into eight genotypes, A to H. Each genotype has a distinct geographic distribution. Three types of viral particles are visualized in infectious serum by electron microscopy. Two of the viral particles are smaller spherical structures with a diameter of 20 nm and filaments of variable lengths with a width of 22 nm. The spheres and filaments are composed of hepatitis B surface antigen (HBsAg) and host-derived lipids without viral nucleic acids and are therefore noninfectious. The infectious HBV virion has a spherical, double-shelled structure 42 nm in diameter. It consists of a lipid envelope containing HBsAg that surrounds an inner nucleocapsid composed of hepatitis B core antigen (HBcAg) complexed with a virally encoded polymerase and the viral DNA genome. The genome of HBV is a partially double-stranded circular DNA of about 3.2 kb pairs. The viral polymerase is covalently attached to the 5′ end of the minus strand.

HBV infection leads to a wide spectrum of liver disease ranging from acute hepatitis to chronic hepatitis, cirrhosis, and hepatocellular carcinoma (HCC). Approximately one-third of adults with acute HBV infection develop clinical symptoms and signs of hepatitis.