Hepatitis b virus

Abstract

Hepatitis B virus (HBV), which may cause self-limited or persistent infections, is a global health problem. It has been estimated that 2 billion people worldwide have been exposed to HBV and 400 million are chronic carriers.. HBV is the prototype of the family Hepadnaviridae. The virion is a spherical particle of 42 nm in diameter composed of a nucleocapsid surrounded by an outer lipoprotein coat, where viral surface antigens are embedded. The genome is a small partially double-stranded relaxed circular DNA, which has a very compact coding organization with four partially overlapping open reading frames that are translated into seven proteins. Although is a DNA virus, like RNA viruses, employs the error-prone polymerase reverse transcriptase as part of its replication process. HBV has been classified into 8 genotypes (A to H) and several subgenotypes. An effective vaccine has been available since the 80s, producing protection in up to 95% of immune competent recipients. The pathogenesis of chronic infection is mainly based on two events: a variety of molecular mechanisms by which the virus interferes with the immune system, preventing its clearance, and successive cycles of inflammation, necrosis and regeneration consequence of the host immune system in an attempt to clarify the infection.