Pathobiology of acute and chronic hepatitis B virus infection: an introduction

The hepatitis B virus (HBV) is a major cause of infectious liver disease throughout the world. According to the Centers for Disease Control, there are 1.2 million carriers of HBV in the USA and approximately 300 million worldwide. The clinical consequences of HBV infection are extremely variable. HBV infection in adults is usually subclinical and after clinically apparent acute hepatitis B infection, approximately 90% of affected adults recover without sequelae, and develop immunity to the virus; however, the clinical course can be quite variable. In another 0.1-0.5% of cases a fulminant hepatitis results in which cell death in the liver is so extensive that fewer than 20-30% of the patients survive. Finally, 5-10% of adults exposed to HBV develop a chronic infection. The nature of the chronic infection is also variable, ranging from hepatocellular necrosis and inflammation (chronic active hepatitis, CAH) to an asymptomatic carrier (ASC) state. In contrast to adult infection, neonatal HBV infection is rarely cleared and over 90% of perinatally infected children become chronically infected. Vertical transmission of HBV is the major source of chronic infection in endemic areas. Chronic HBV infection is associated with hepatocellular carcinoma (HCC). In fact, the risk of HCC is 100-fold in patients with chronic HBV infection.