Viral hepatitis.

Abstract

Hepatitis A is still the most frequently reported vaccine preventable disease. A reduction in the incidence will only be achieved by routine childhood vaccination rather than by targeted vaccination of high-risk groups. A larger vaccine program is warranted. Hepatitis B remains a large public health problem. Vaccination targeted to high-risk adults failed to decrease the incidence of hepatitis B virus (HBV) infection. Sexual as well as nosocomial transmission remain serious problems. Vaccine escape variants have also been identified in newborns from infected mothers who had been vaccinated at birth. Clearance of HBV infection results from complex immune mechanisms including TH1 cytokines significantly associated with HLA class II alleles. Escape HBV mutants, especially precore mutants, influence the outcome. The sequences of the promoter and other critical regions were associated with severe activity. Lamivudine is a major advance in therapy of chronic hepatitis B which was recently approved in many countries. Although drug resistant mutants may be selected during therapy, additional nucleoside analogues including adefovir are promising. Optimal combination strategies of different active compounds need to be researched. Three per cent of the world population has been infected with hepatitis C virus (HCV). Epidemiology has shifted from transfusion to non-transfusion settings. Intravenous drug abuse is currently the main risk but nosocomial infection is also of concern. Three independent factors seem associated with fibrosis progression: age, daily alcohol consumption of 50 g or more and male gender. Median duration of progression to cirrhosis is about 30 years. At the cirrhotic stage, about 3-5% of patients per year develop hepatocellular carcinoma. There is little evidence that direct cytopathicity plays a significant role in liver cell injury. HCV also infects extrahepatic cells which seems critical in the pathogenesis of the many extrahepatic manifestations. The recent identification of CD81 protein as one of the HCV receptor candidates may help us to understand how chronic HCV infection may trigger a wide spectrum of clinical manifestations, autoimmune or even lymphoproliferative, through potent continuous B cell activation in the context of various host and/or environmental cofactors. Direct measurement of HCV RNA has clarified HCV replication kinetics and variability. Among patients with chronic hepatitis C, 48 weeks of treatment with interferon/ribavirin therapy produced a response rate of 28% among those with genotype 1 and 66% with other genotypes. Similar differences were found for combination therapy among patients who had relapsed following previous interferon (IFN) therapy. Viral load prior to treatment has been clearly shown to be predictive of response to interferon treatment, with increased viral load associated with decrease rates of response. In patients non-responsive to interferon, a second course of interferon alone has no beneficial effect whereas combination therapy may induce response in 25%. In conclusion, combination therapy should be given in all situations. Viral eradication should not be the only objective of the treatment since histological improvement may be obtained despite persisting viral replication with prolonged maintenance of antiviral therapy.