Hepatitis B virus

Hepatitis B virus (HBV) is a partially double-stranded DNA virus, a species of the genus Orthohepadnavirus and a member of the Hepadnaviridae family of viruses. This virus causes the disease hepatitis B. Hepatitis B virus is classified in the genus Orthohepadnavirus, which contains 11 other species. The genus is classified as part of the Hepadnaviridae family, which contains four other genera, Avihepadnavirus, Herpetohepadnavirus, Metahepadnavirus and Parahepadnavirus. This family of viruses is the only member of the viral order Blubervirales. Viruses similar to hepatitis B have been found in all apes (orangutans, gibbons, bonobos, gorillas and chimpanzees), in Old World monkeys, and in New World woolly monkeys (the woolly monkey hepatitis B virus), suggesting an ancient origin for this virus in primates. The virus is divided into four major serotypes (adr, adw, ayr, ayw) based on antigenic epitopes present on its envelope proteins. These serotypes are based on a common determinant (a) and two mutually exclusive determinant pairs (d/y and w/r). The viral strains have also been divided into ten genotypes (A–J) and forty subgenotypes according to overall nucleotide sequence variation of the genome. The genotypes have a distinct geographical distribution and are used in tracing the evolution and transmission of the virus. Differences between genotypes affect the disease severity, course and likelihood of complications, and response to treatment. The serotypes and genotypes do not necessarily correspond. Genotype D has 10 subgenotypes. A number of as yet unclassified hepatitis B-like species have been isolated from bats. Hepatitis B virus is a member of the Hepadnavirus family. The virus particle, called Dane particle (virion), consists of an outer lipid envelope and an icosahedral nucleocapsid core composed of protein. The nucleocapsid encloses the viral DNA and a DNA polymerase that has reverse transcriptase activity similar to retroviruses. The outer envelope contains embedded proteins which are involved in viral binding of, and entry into, susceptible cells.