[Natural history of hepatitis B infection]

Hepatitis B virus (HBV) is transmitted by parenteral, sexual and perinatal routes. While fulminant hepatitis may occur in 1% of cases of symptomatic acute hepatitis, the principal problem of HBV infection is that it may become chronic, classically defined by carriage of HB surface antigens (HBsAg) for more than 6 months. This occurs in only 0.5 to 3% of immunocompetent adults but more frequently in children (up to 90%) and in immune-compromised patients (30 to 100%). The course of chronic HBV infection is characterized by variations in viral replication with spontaneous reactivation or discontinuation, and potential exacerbations observed clinically or by laboratory testing. The pathogenesis of HBV infection is mainly immune-mediated, resulting from host-virus interactions but also from the complexity of the virus itself (integration, mutation, occult replication). These factors explain the variety of presentations of chronic HBV infection, which range from immune tolerance to inactive carriage of HBsAg, passing through a stage of immune clearance, where chronic active hepatitis which may lead to cirrhosis (yearly incidence of 1.3 to 5.9%). Cirrhosis may be complicated by portal hypertension, liver failure, or hepatocellular carcinoma, which together explain 80% of the morbidity and mortality associated with HBV. The 5-year survival rate for HBV-related cirrhosis ranges from 52 to 82%. Immunosuppression, hepatitis D virus superinfection, and chronic alcohol consumption are the principal factors that modify this natural history. Chronic HBV infection is a major public health problem, particularly in developing countries, and it requires that efforts to make HBV vaccination universal be intensified.