[Epidemiology and natural history of hepatitis B].

The transmission of the hepatitis B virus (HBV) is parenteral, sexual and perinatal. If a fulminant hepatitis may occur in 1% of cases of symptomatic acute hepatitis, the main problem of HBV infection is its chronicity, as defined by HBs antigen carriage for more than 6 months. It occurs in only 0.5 to 3% of immunocompetent adults but more frequently in children (up to 90%) or in immunocompromised patients (30 to 100%). Evolution of HBV chronic infection is characterized by variations of viral replication with spontaneous reactivations or discontinuations with potential clinical and biochemical exacerbations. Pathogeny of HBV infection is mainly immune-mediated, resulting from the host-virus interactions but also from the complexity of HBV (integration, mutation, occult replication), explaining the polymorphism of chronic HBV infection; it includes immune tolerance, inactive carriage of HBs antigen but also immune elimination with chronic active hepatitis which may lead to cirrhosis (yearly incidence of 1.3 to 5.9%). Cirrhosis may result in complications of portal hypertension and liver failure or hepatocellular carcinoma which explain 80% of morbidity and mortality of HBV: the 5-year survival of HBV-related cirrhosis ranges from 52 to 82%. Immunosuppression, delta virus superinfection or chronic alcohol consumption are the main factors which modify the natural history of HBV infection. HBV chronic infection is a problem of public health, particularly in developing countries, evidencing the need for universal HBV vaccination.