WordNet
- a group of animal DNA viruses including viruses of ducks and woodchucks and squirrels and others as well as the virus causing hepatitis B in humans
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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2012/08/03 10:05:51」(JST)
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| Hepadnaviridae | |
|---|---|
| TEM micrograph showing hepatitis B virions | |
| Virus classification | |
| Group: | Group VII (dsDNA-RT) |
| Order: | Unassigned |
| Family: | Hepadnaviridae |
| Genera | |
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Orthohepadnavirus |
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Hepadnaviruses are a family of viruses which can cause liver infections in humans and animals. There are two recognized genera:
- Genus Orthohepadnavirus; type species: Hepatitis B virus
- Genus Avihepadnavirus; type species: Duck hepatitis B virus
The name of the family comes from : hepa(for HEPAtic)-DNA-virus.
Contents
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Virology
Genome
Hepadnaviruses have very small genomes of partially double-stranded, partially single stranded circular DNA. The genome consists of two uneven strands of DNA. One has a negative-sense orientation, and the other, shorter, strand has a positive-sense orientation.
As it is a group 7 virus, replication involves an RNA intermediate. Three main open reading frames are encoded (ORFs) and the virus has four known genes which encode the core protein, the virus polymerase, surface antigens (preS1, preS2, and S) and the X protein. The X protein is thought to be non-structural; however, its function and significance are poorly understood.
Replication
Hepadnaviruses replicate through an RNA intermediate (which they transcribe back into cDNA using reverse transcriptase). The reverse transcriptase becomes covalently linked to a short 3- or 4-nucleotide primer.[1] Most hepadnaviruses will only replicate in specific hosts, and this makes experiments using in vitro methods very difficult.
The virus binds to specific receptors on cells and the core particle enters the cell cytoplasm. This is then translocated to the nucleus, where the partially double stranded DNA is 'repaired' by the cell to form a complete circle of DNA. It then undergoes transcription by the host cell RNA polymerase and the transcript is translated by host cell ribosomes. New virus particles are formed, which acquire lipid from the endoplasmic reticulum of the host cell, and the genome is packaged within these particles, which then bud off from the cell.
Hepadnavirus-infected cells translate the protein known as the virus surface antigen many times until there is too much protein to coat the virions formed. These proteins then aggregate to form rod shapes, and it is this antigen, known as the Australian or hepatitis B surface antigen, which is released from the cell and which leads to a very strong immune response from the host.
Medical aspects
Prognosis
It is thought that most of the people who come into contact with the virus are able to clear the infection alone; however, there are some who cannot, and these patients progress to fulminant hepatitis. This condition causes severe liver damage and, in very rare cases, may also lead to primary hepatocellular carcinoma.[2]
Treatment
The treatment for hepatitis B includes a course of alpha interferon; this is a very expensive treatment which lasts for around 12–15 weeks and makes the patient very sick. It seems that the interferon treatment aims at kick-starting the host immune response to clear the infection; it is not the drugs that clear the infection. There are reverse transcriptase inhibitors available as treatment; these drugs target the virus replication strategy by (as the name suggests) inhibiting reverse transcription. Hepatitis B infection can also be prevented by means of a recombinant Hepatitis B surface antigen vaccine.
References
- ^ A Novel cis-Acting Element Facilitates Minus-Strand DNA Synthesis during Reverse Transcription of the Hepatitis B Virus Genome by Myeong-Kyun Shin, Jehan Lee and Wang-Shick Ryu in Journal of Virology (2004) volume 78, pages 6252–6262.
- ^ [1]
External links
- Viralzone: Hepadnaviridae
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UpToDate Contents
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- 1. B型肝炎ウイルス遺伝子型の臨床的意義 clinical significance of hepatitis b virus genotypes
- 2. 一般的なB型肝炎ウイルス亜種の臨床的意義および分子学的特徴 clinical significance and molecular characteristics of common hepatitis b virus variants
Japanese Journal
- Inhibition of cellular proteasome activities enhances hepadnavirus replication in an HBX-dependent manner
- ZHANG Z
- J Virol 78, 4566-4572, 2004
- NAID 30020799872
- Long-term high-dose interferon-alpha therapy delays Hepadnavirus-related hepatocarcinogenesis in X/myc transgenic mice
- MERLE P
- Oncogene 22, 2762-2771, 2003
- NAID 30013807485
Related Pictures
★リンクテーブル★
| リンク元 | 「ヘパドナウイルス」 |