Poxviridae
Poxviridae | |
---|---|
Virus classification | |
(unranked): | Virus |
Realm: | Varidnaviria |
Kingdom: | Bamfordvirae |
Phylum: | Nucleocytoviricota |
Class: | Pokkesviricetes |
Order: | Chitovirales |
Family: | Poxviridae |
Subfamilies | |
Poxviridae is a family of double-stranded
Four genera of poxviruses may infect humans:
Etymology
The name of the family, Poxviridae, is a legacy of the original grouping of viruses associated with diseases that produced poxes on the skin. Modern viral classification is based on phenotypic characteristics; morphology, nucleic acid type, mode of replication, host organisms, and the type of disease they cause. The smallpox virus remains the most notable member of the family.[citation needed]
History
Diseases caused by pox viruses, especially smallpox, have been known about for centuries. One of the earliest suspected cases is that of Egyptian
A century after Edward Jenner showed that the less potent cowpox could be used to effectively vaccinate against the more deadly smallpox, a worldwide effort to vaccinate everyone against smallpox began with the ultimate goal to rid the world of the plague-like epidemic.[citation needed] The last case of endemic smallpox occurred in Somalia in 1977. Extensive searches over two years detected no further cases, and in 1979 the World Health Organization (WHO) declared the disease officially eradicated.[citation needed]
In 1986, all virus samples were destroyed or transferred to two approved WHO reference labs: at the headquarters of the federal Centers for Disease Control and Prevention (the C.D.C.) in Atlanta, Georgia (the United States) and at the Institute of Virus Preparations in Moscow.[6] After September 11, 2001 the American and UK governments have had increased concern over the use of smallpox, or a smallpox-like disease, in bioterrorism. However, several poxviruses including vaccinia virus, myxoma virus, tanapox virus and raccoon pox virus are currently being investigated for their therapeutic potential in various human cancers in preclinical and clinical studies.[7][8][9]
Microbiology
Structure
Poxviridae viral particles (virions) are generally
Genome
Phylogenetic analysis of 26 different
The GC-content of family member genomes differ considerably.[13] Avipoxvirus, capripoxvirus, cervidpoxvirus, orthopoxvirus, suipoxvirus, yatapoxvirus and one Entomopox genus (Betaentomopoxvirus) along with several other unclassified Entomopoxviruses have a low G+C content while others - Molluscipoxvirus, Orthopoxvirus, Parapoxvirus and some unclassified Chordopoxvirus - have a relatively high G+C content. The reasons for these differences are not known.[citation needed]
Replication
Replication of the poxvirus involves several stages.[14] The virus first binds to a receptor on the host cell surface; the receptors for the poxvirus are thought to be glycosaminoglycans.[citation needed] After binding to the receptor, the virus enters the cell where it uncoats.[citation needed] Uncoating of the virus is a two step process.[citation needed] Firstly the outer membrane is removed as the particle enters the cell; secondly the virus particle (without the outer membrane) fuses with the cellular membrane to release the core into the cytoplasm.[citation needed] The pox viral genes are expressed in two phases.[citation needed] The early genes encode the non-structural protein, including proteins necessary for replication of the viral genome, and are expressed before the genome is replicated.[citation needed] The late genes are expressed after the genome has been replicated and encode the structural proteins to make the virus particle.[citation needed] The assembly of the virus particle occurs in five stages of maturation that lead to the final exocytosis of the new enveloped virion.[citation needed] After the genome has been replicated, the immature virion assembles the A5 protein to create the intracellular mature virion.[citation needed] The protein aligns and the brick-shaped envelope of the intracellular enveloped virion.[citation needed] These particles are then fused to the cell plasma to form the cell-associated enveloped virion, which encounters the microtubules and prepares to exit the cell as an extracellular enveloped virion.[citation needed] The assembly of the virus particle occurs in the cytoplasm of the cell and is a complex process that is currently being researched to understand each stage in more depth.[citation needed] Considering the fact that this virus is large and complex, replication is relatively quick taking approximately 12 hours until the host cell dies by the release of viruses.[citation needed]
The replication of poxvirus is unusual for a virus with double-stranded DNA genome because it occurs in the cytoplasm,[15] although this is typical of other large DNA viruses.[16] Poxvirus encodes its own machinery for genome transcription, a DNA dependent RNA polymerase,[17] which makes replication in the cytoplasm possible. Most double-stranded DNA viruses require the host cell's DNA-dependent RNA polymerase to perform transcription. These host polymerases are found in the nucleus, and therefore most double-stranded DNA viruses carry out a part of their infection cycle within the host cell's nucleus.[citation needed]
Evolution
The ancestor of the poxviruses is not known but structural studies suggest it may have been an adenovirus or a species related to both the poxviruses and the adenoviruses.[18]
Based on the genome organisation and DNA replication mechanism a phylogenetic relationships may exist between the rudiviruses (Rudiviridae) and the large eukaryal DNA viruses: the African swine fever virus (Asfarviridae), Chlorella viruses (Phycodnaviridae) and poxviruses (Poxviridae).[19]
The mutation rate in poxvirus genomes has been estimated to be 0.9–1.2 x 10−6 substitutions per site per year.[20] A second estimate puts this rate at 0.5–7 × 10−6 nucleotide substitutions per site per year.[21] A third estimate places the rate at 4–6 × 10−6.[22]
The last common ancestor of the extant poxviruses that infect vertebrates existed 0.5 million years ago. The genus Avipoxvirus diverged from the ancestor 249 ± 69 thousand years ago. The ancestor of the genus Orthopoxvirus was next to diverge from the other clades at 0.3 million years ago. A second estimate of this divergence time places this event at 166,000 ± 43,000 years ago.[21] The division of the Orthopoxvirus into the extant genera occurred ~14,000 years ago. The genus Leporipoxvirus diverged ~137,000 ± 35,000 years ago. This was followed by the ancestor of the genus Yatapoxvirus. The last common ancestor of the Capripoxvirus and Suipoxvirus diverged 111,000 ± 29,000 years ago.[citation needed]
An isolate from a fish – salmon gill poxvirus – appears to be the earliest branch in the Chordopoxvirinae.[23] A new systematic has been proposed recently after findings of a new squirrel poxvirus in Berlin, Germany.[24]
Smallpox
The date of the appearance of smallpox is not settled. It most likely evolved from a rodent virus between 68,000 and 16,000 years ago.[25][26] The wide range of dates is due to the different records used to calibrate the molecular clock. One clade was the variola major strains (the more clinically severe form of smallpox) which spread from Asia between 400 and 1,600 years ago. A second clade included both alastrim minor (a phenotypically mild smallpox) described from the American continents and isolates from West Africa which diverged from an ancestral strain between 1,400 and 6,300 years before present. This clade further diverged into two subclades at least 800 years ago.[citation needed]
A second estimate has placed the separation of variola from
Taxonomy
The species in the subfamily Chordopoxvirinae infect vertebrates and those in the subfamily Entomopoxvirinae infect insects. There are ten recognised genera in the Chordopoxvirinae and three in the Entomopoxvirinae.
The following subfamilies and genera are recognized (-virinae denotes subfamily and -virus denotes genus):[2]
- Avipoxvirus
- Capripoxvirus
- Centapoxvirus
- Cervidpoxvirus
- Crocodylidpoxvirus
- Leporipoxvirus
- Macropopoxvirus
- Molluscipoxvirus
- Mustelpoxvirus
- Orthopoxvirus
- Oryzopoxvirus
- Parapoxvirus
- Pteropopoxvirus
- Salmonpoxvirus
- Sciuripoxvirus
- Suipoxvirus
- Vespertilionpoxvirus
- Yatapoxvirus
- Alphaentomopoxvirus
- Betaentomopoxvirus
- Deltaentomopoxvirus
- Diachasmimorpha entomopoxvirus
- Gammaentomopoxvirus
Both subfamilies also contain a number of unclassified species for which new genera may be created in the future.
- Cotia virus of 2012 is an unusual chordopoxvirus that may belong to a new genus.[27] Cotia virus was assigned the new genus Oryzopoxvirus in 2019.[28] A Brazilian porcupinepox virus discovered in 2019 is closely related to the virus.[29]
- Two more chordopoxviruses are NY_014 and murmansk poxvirus. They are considered closely related to a "Yoka poxvirus".[30] ICTV classifies them under a genus Centapoxvirus, created 2016.[31]
Vaccinia virus
The prototypical poxvirus is
Vaccinia contains three classes of genes: early, intermediate and late. These genes are transcribed by viral RNA polymerase and associated transcription factors. Vaccinia replicates its genome in the cytoplasm of infected cells, and after late-stage gene expression undergoes virion morphogenesis, which produces intracellular mature virions contained within an envelope membrane. The origin of the envelope membrane is still unknown. The intracellular mature virions are then transported to the Golgi apparatus where it is wrapped with an additional two membranes, becoming the intracellular enveloped virus. This is transported along cytoskeletal microtubules to reach the cell periphery, where it fuses with the plasma membrane to become the cell-associated enveloped virus. This triggers actin tails on cell surfaces or is released as external enveloped virion.[citation needed]
See also
- Quokkapox virus
- Water warts
References
- ^ "Viral Zone". ExPASy. Retrieved 15 June 2015.
- ^ a b "Virus Taxonomy: 2019 Release". talk.ictvonline.org. International Committee on Taxonomy of Viruses. Retrieved 9 May 2020.
- ^ "Pathogenic Molluscum Contagiosum Virus Sequenced". Antiviral Agents Bulletin: 196–7. August 1996. Retrieved 16 July 2006.
- ^ Hopkins, Donald R. (2002) [1983]. The greatest killer: smallpox in history, with a new introduction. University of Chicago Press. p. 15.
By special permission of the late President Anwar el Sadat, I was allowed to examine the front upper half of Ramses V's unwrapped mummy in the Cairo Museum in 1979. …Inspection of the mummy revealed a rash of elevated "pustules," each about two to four millimeters in diameter, …(An attempt to prove that this rash was caused by smallpox by electron-microscopic examination of tiny pieces of tissue that had fallen on the shroud was unsuccessful. I was not permitted to excise one of the postules.) …The appearance of the larger pustules and the apparent distribution of the rash are similar to smallpox rashes I have seen in more recent victims
- ISBN 0816045631p.337.
- PMID 10367824.
- PMID 25839047.
- PMID 20160706.
- PMID 32930107.
- ^ International Committee on Taxonomy of Viruses (15 June 2004). "ICTVdb Descriptions: 58. Poxviridae". Retrieved 26 February 2005.
- ^ How Big is a ... ? at Cells Alive!. Retrieved 2005-02-26.
- PMID 14718625.
- S2CID 21779605.
- ^ "Orthopoxvirus replication ~ ViralZone". viralzone.expasy.org. Retrieved 26 June 2022.
- PMID 20231474..
- ^ Racaniello, Vincent (4 March 2014). "Pithovirus: Bigger than Pandoravirus with a smaller genome". Virology Blog. Retrieved 4 March 2014.
- ^ National Center for Infectious Diseases, Centers for Disease Control and Prevention, 1600 Clifton Rd., Atlanta, GA 30333, USA. "DNA-dependent RNA polymerase rpo35 (Vaccinia virus)". National Center for Biotechnology Information (NCBI), NIH, Bethesda, MD, USA.
{{cite web}}
: CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link) - PMID 21742267.
- S2CID 20018642.
- ^ Babkin IV, Shchelkunov SN (2006) The time scale in poxvirus evolution. Mol Biol (Mosk) 40(1):20-24
- ^ PMID 21228539.
- ^ PMID 19833230.
- PMID 26136578.
- PMID 28930029.(for systematic see figure 2)
- S2CID 39823899.
- PMID 17901212.
- ^ Afonso PP, Silva PM, Schnellrath LC, Jesus DM, Hu J, Yang Y, Renne R, Attias M, Condit RC, Moussatché N, Damaso CR (2012) Biological characterization and next-generation genome sequencing of the unclassified Cotia virus SPAn232 (Poxviridae). J Virol
- ^ "Taxonomy History [Cotia virus] - Taxonomy - ICTV". talk.ictvonline.org.
- PMID 33754985.
- ^ Smithson C, Meyer H, Gigante CM, Gao J, Zhao H, Batra D, Damon I, Upton C, Li Y (2017) Two novel poxviruses with unusual genome rearrangements: NY_014 and Murmansk. Virus Genes
- ^ "Taxonomy History [Yokapox virus] - Taxonomy - ICTV". talk.ictvonline.org.
External links
- Electron micrographs of Orthopoxvirus and Parapoxvirus Genera, including the smallpox virus, have been collected by the International Committee on Taxonomy of Viruses in their Poxviridae picture gallery.
- Buller, R. Mark L.; Palumbo, Gregory J. (1991). "Poxvirus Pathogenesis". Microbiology and Molecular Biology Reviews. 55 (1): 80–122. PMID 1851533.
- NCBI Taxonomy Page.
- Poxviridae at the Viral Bioinformatics Resource Center.
- Viralzone: Poxviridae
- ICTV
- Virus Pathogen Database and Analysis Resource (ViPR): Poxviridae