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Figure 1. Structure of hepatitis B virus genome. The genome of HBV is a double-stranded circular DNA (3.2 kb), which contains four open reading frames coding for polymerase (P), surface antigens (PreS1, PreS2, and S), pre-core (preC), core (C) and X. bp: Base pair; HBV: Hepatitis B virus.
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Figure 2. Hepatitis B virus life cycle. Entry of the HBV virion into hepatocytes is a poorly defined process. HBV replicates in the hepatocytes to produce HBsAg particles and virions. The antigens can be recognized by CD8+ or CD4+ T cells, respectively. This recognition reaction can lead to either direct lysis of the infected hepatocyte or the release of IFN and TNF-α, which can downregulate viral replication in surrounding hepatocytes without direct cell killing. ccc: Covalently closed circular; ER: Endoplasmic reticulum; HBsAg: Hepatitis B surface antigen; HBV: Hepatitis B virus; IFN: Interferon; MHC: Major histocompatibility complex; pRNA: Packaging RNA; TNF: Tumor necrosis factor.
(Figure omitted. See article PDF.)
Molecular epidemiology
Hepatitis B virus (HBV), discovered in 1966, has infected more than 350 million people worldwide. The infection of HBV is a leading cause of chronic hepatitis, liver cirrhosis (LC) and hepatocellular carcinoma (HCC), accounting for 1 million deaths annually. Chronic HBV patients can fluctuate between periods of active liver inflammation and periods of inactive disease. Disease progression can be influenced by various factors [1]. Transmission occurs via perinatal, sexual and parenteral routes, particularly intravenous drug abuse and, while blood products still carry a risk, this is now extremely low in Western countries. Only a minority of infected adult cases are able to develop chronic hepatitis but, in children under 1 year of age, 90% develop chronic hepatitis [2]. The distribution of HBV infection varies greatly throughout the world. The prevalence is high in some areas, such as South-East Asia, China and Africa. Areas with low levels of endemicity include North America, Western Europe and Australia. HCC is almost always associated with LC in China. In both high- and low-incidence areas, HCC predominates in males, with male-to-female ratios of 3-4:1.
Virological characteristics
HBV is the prototype member of the Hepadnaviridae family and consists of a circular, partially double-stranded DNA molecule of 3.2 kb in length containing four overlapping reading frames...