Epidemiology and immunopathogenesis of chronic hepatitis B virus infection

Hepatitis B virus (HBV) infection has global health implications. Approximately 5% of the world population consists of chronic HBV carriers, of which one-quarter to one-third will develop progressive liver disease. The prevalence of HBV varies widely, with high endemic regions in Asia and sub-Saharan Africa to low endemic regions in Western Europe and the United States. The main method of transmission of HBV varies with perinatal and sexual transmission as the predominant routes in high- and low-prevalence regions, respectively. The transition from acute infection to the chronic carrier state appears to be immunologically mediated. A strong humoral and cellular immune response are characteristic of resolved infections, whereas a weak antiviral immune response is observed in chronic HBV infection. The immunologic processes by which chronic HBV infection develops remain to be elucidated. Animal models of HBV infection, however, may help to define immunologic mechanisms that underlie chronic infection.