INTRODUCTION TO EPIDEMIOLOGY AND RISK OF HEPATITIS-B

The most important modes of transmission of hepatitis B virus (HBV) ar e sexual, needle stick (both accidental or through intravenous drug us e), blood transfusion or from mothers to newborns. The outcome of HBV infection mainly depends on the immune response of the host but is als o influenced by the capability of the virus to escape defence mechanis ms by integration into the genome of the host's hepatocytes. These fac tors affect whether HBV infection leads to acute hepatitis or remains asymptomatic, whether the infection resolves to immunity or becomes ch ronic and whether chronic clinical sequellae such as chronic hepatitis , liver cirrhosis or hepatocellular carcinoma develop. The epidemiolog ical status of a given country with regard to HBV depends on socioecon omic factors, the proportion of individuals with risky life styles, th e pre-existing prevalence of HBV, the vaccine programme available and compliance to hygienic measures.