Present knowledge of viral hepatitis

The term viral hepatitis refers to the diseases produced by at least three, and perhaps four or five aetiologic agents that differ in their virologic characteristics, ecologic mechanisms, epidemiologic patterns, and long term consequences. These divergences are now well-defined for hepatitis A virus (HAV) and hepatitis B virus (HBV). HAV is an RNA virus dependent upon consecutive transmission in childhood, and is not associated with long term sequelae. In contrast, HBV is a DNA virus capable of producing a reservoir of chronic human infection from which spread to adults as well as children can periodically occur by a variety of methods. Chronic HBV disease is not only a continuing source of potential viral transmission in the community, but also sometimes results years later in very serious consequences. Continuing destruction of the liver leads to cirrhosis and hepatic failure; in addition, integration of viral DNA into that of the hepatocyte is probably responsible for the high incidence of carcinoma of the liver associated with HBV infection in many areas of the world. The 'third' form of viral hepatitis is termed 'non-A, non-B' (NANB), because it is identified only by serologic exclusion of HAV and HBV infection. Its epidemiologic and clinical characterization are difficult because variations in behaviour in groups of cases suggest that more than one virus is responsible for this negatively defined entity. One or more of the agents leads to chronic infection, but the relative frequency with which it causes chronic active hepatitis or hepatocellular carcinoma cannot yet be stated.