Human hepatitis B virus (HBV), family Hepadnaviridae, is highly infectious and is transmitted by blood and body fluids. It is estimated that over 250 million persons worldwide have chronic HBV infection, putting them at increased risk for developing cirrhosis of the liver and hepatocellular carcinoma. The course of HBV infection is highly dependent on the age of the infected individual. Among adults, ~90% will clear the infection within 6 months but ~10% will develop lifelong chronic infection. The clinical outcome is reversed among infants with most becoming chronic carriers. HBV is a small, enveloped virus with a T=4 icosahedral capsid. Hepadnavirus genomes are relaxed circles of partially double-stranded DNA, synthesized by reverse transcription during virion assembly in the infected cell. Hepadnavirus replication is largely restricted to differentiated hepatocytes and infection is noncytopathic.
