Hepadnaviridae

Hepadnaviridae is a family of small enveloped DNA viruses that infect the liver cells of vertebrates, and it is the only accepted family in the order Blubervirales. Its five recognised genera are Avihepadnavirus, Orthohepadnavirus, Herpetohepadnavirus, Metahepadnavirus and Parahepadnavirus. Natural hosts include humans, apes and birds, and the best-known member is hepatitis B virus, which causes hepatitis, cirrhosis and, in chronic infection, hepatocellular carcinoma. Virions are spherical with T=4 symmetry and about 42 nanometres across, and the circular genome of around 3.2 kilobases is partly double stranded and codes for seven proteins. Replication runs through an RNA intermediate that the virus's own polymerase copies back into DNA by reverse transcription, and new virions leave the cell by budding. Hepadnaviruses are thought to be ancient: related sequences are found in the genomes of birds, crocodilians, snakes and turtles, and the family has apparently co-evolved with vertebrates.