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''Poxviridae'' is a family of double-stranded DNA
viruses A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Since Dmitri Ivanovsky's ...
.
Vertebrate Vertebrates () comprise all animal taxon, taxa within the subphylum Vertebrata () (chordates with vertebral column, backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the ...
s and
arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chitin, o ...
s serve as natural hosts. There are currently 83 species in this family, divided among 22 genera, which are divided into two subfamilies. Diseases associated with this family include
smallpox Smallpox was an infectious disease caused by variola virus (often called smallpox virus) which belongs to the genus Orthopoxvirus. The last naturally occurring case was diagnosed in October 1977, and the World Health Organization (WHO) cer ...
. Four genera of poxviruses may infect humans: ''
Orthopoxvirus ''Orthopoxvirus'' is a genus of viruses in the family ''Poxviridae'' and subfamily ''Chordopoxvirinae''. Vertebrates, including mammals and humans, and arthropods serve as natural hosts. There are 12 species in this genus. Diseases associated wi ...
'', ''
Parapoxvirus ''Parapoxvirus'' is a genus of viruses, in the family ''Poxviridae'', in the subfamily ''Chordopoxvirinae''. Like all members of the family Poxviridae, they are oval, relatively large, double-stranded DNA viruses. Parapoxviruses have a unique sp ...
'', ''
Yatapoxvirus ''Yatapoxvirus'' is a genus of viruses, in the family ''Poxviridae'', in the subfamily ''Chordopoxvirinae''. Monkeys and baboons serve as natural hosts. There are two species in this genus. Diseases associated with this genus include: histiocyto ...
'', ''
Molluscipoxvirus ''Molluscum contagiosum virus'' (MCV) is a species of DNA poxvirus that causes the human skin infection molluscum contagiosum. Molluscum contagiosum affects about 200,000 people a year, about 1% of all diagnosed skin diseases. Diagnosis is base ...
''. ''Orthopoxvirus'':
smallpox Smallpox was an infectious disease caused by variola virus (often called smallpox virus) which belongs to the genus Orthopoxvirus. The last naturally occurring case was diagnosed in October 1977, and the World Health Organization (WHO) cer ...
virus (variola),
vaccinia ''Vaccinia virus'' (VACV or VV) is a large, complex, enveloped virus belonging to the poxvirus family. It has a linear, double-stranded DNA genome approximately 190 kbp in length, which encodes approximately 250 genes. The dimensions of the ...
virus,
cowpox Cowpox is an infectious disease caused by the ''cowpox virus'' (CPXV). It presents with large blisters in the skin, a fever and swollen glands, historically typically following contact with an infected cow, though in the last several decades more ...
virus,
monkeypox Monkeypox (also called mpox by the WHO) is an infectious viral disease that can occur in humans and some other animals. Symptoms include fever, swollen lymph nodes, and a rash that forms blisters and then crusts over. The time from exposure ...
virus; ''Parapoxvirus'': orf virus,
pseudocowpox Pseudocowpox is a disease caused by the Paravaccinia virus or Pseudocowpox virus, a virus of the family ''Poxviridae'' and the genus '' Parapoxvirus''. Humans can contract the virus from contact with livestock infected with Bovine papular stomat ...
,
bovine papular stomatitis Bovine papular stomatitis is a farmyard pox caused by ''Bovine papular stomatitis virus'' (BPSV), which can spread from infected cattle to cause disease in milkers, farmers and veterinarians. Generally there is usually one or a few skin lesions t ...
virus; ''Yatapoxvirus'':
tanapox Tanapox (a virus from the genus ''Yatapoxvirus'') was first seen among individuals in the flood plain of the Tana River in Kenya during two epidemics (1957 and 1962) of acute febrile illness accompanied by localized skin lesions. Signs and sym ...
virus,
yaba monkey tumor virus The Yaba monkey tumor virus is a type of poxvirus. The first case of the virus was obtained from a colony of rhesus monkeys in Yaba, Lagos, Nigeria Nigeria ( ), , ig, Naìjíríyà, yo, Nàìjíríà, pcm, Naijá , ff, Naajeeriya, kcg ...
; ''Molluscipoxvirus'':
molluscum contagiosum virus ''Molluscum contagiosum virus'' (MCV) is a species of DNA poxvirus that causes the human skin infection molluscum contagiosum. Molluscum contagiosum affects about 200,000 people a year, about 1% of all diagnosed skin diseases. Diagnosis is based ...
(MCV). The most common are vaccinia (seen on the Indian subcontinent) and molluscum contagiosum, but monkeypox infections are rising (seen in west and central African rainforest countries). The similarly named disease
chickenpox Chickenpox, also known as varicella, is a highly contagious disease caused by the initial infection with varicella zoster virus (VZV). The disease results in a characteristic skin rash that forms small, itchy blisters, which eventually scab ...
is not a true poxvirus and is caused by the
herpesvirus ''Herpesviridae'' is a large family of DNA viruses that cause infections and certain diseases in animals, including humans. The members of this family are also known as herpesviruses. The family name is derived from the Greek word ''ἕρπει� ...
varicella zoster Varicella-zoster virus (VZV), also known as human herpesvirus 3 (HHV-3, HHV3) or ''Human alphaherpesvirus 3'' ( taxonomically), is one of nine known herpes viruses that can infect humans. It causes chickenpox (varicella) commonly affecting chi ...
.


Etymology

The name of the family, ''Poxviridae'', is a legacy of the original grouping of viruses associated with diseases that produced poxes in 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 Smallpox was an infectious disease caused by variola virus (often called smallpox virus) which belongs to the genus Orthopoxvirus. The last naturally occurring case was diagnosed in October 1977, and the World Health Organization (WHO) cer ...
virus remains the most notable member of the family.


History

Diseases caused by pox viruses, especially smallpox, have been known about for centuries. One of the earliest suspected cases is that of Egyptian
pharaoh Pharaoh (, ; Egyptian: '' pr ꜥꜣ''; cop, , Pǝrro; Biblical Hebrew: ''Parʿō'') is the vernacular term often used by modern authors for the kings of ancient Egypt who ruled as monarchs from the First Dynasty (c. 3150 BC) until the ...
Ramses V Usermaatre Sekheperenre Ramesses V (also written Ramses and Rameses) was the fourth pharaoh of the Twentieth Dynasty of Egypt and was the son of Ramesses IV and Duatentopet. Reign Ramesses V's reign was characterized by the continued growth of ...
who is thought to have died from smallpox circa 1150 years BCE. Smallpox was thought to have been transferred to Europe around the early 8th century and then to the
Americas The Americas, which are sometimes collectively called America, are a landmass comprising the totality of North and South America. The Americas make up most of the land in Earth's Western Hemisphere and comprise the New World. Along with t ...
in the early 16th century, resulting in the deaths of 3.2 million
Aztecs The Aztecs () were a Mesoamerican culture that flourished in central Mexico in the post-classic period from 1300 to 1521. The Aztec people included different ethnic groups of central Mexico, particularly those groups who spoke the Nahuatl l ...
within two years of introduction. This death toll can be attributed to the indigenous population's complete lack of exposure to the virus over millennia. A century after
Edward Jenner Edward Jenner, (17 May 1749 – 26 January 1823) was a British physician and scientist who pioneered the concept of vaccines, and created the smallpox vaccine, the world's first vaccine. The terms ''vaccine'' and ''vaccination'' are derived f ...
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. 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 The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of h ...
(WHO) declared the disease officially eradicated. 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 Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services, and is headquartered in Atlanta, Georg ...
(the C.D.C.) in
Atlanta Atlanta ( ) is the capital and most populous city of the U.S. state of Georgia. It is the seat of Fulton County, the most populous county in Georgia, but its territory falls in both Fulton and DeKalb counties. With a population of 498,715 ...
, Georgia (the United States) and at the Institute of Virus Preparations in Moscow. 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.


Microbiology


Structure

''Poxviridae'' viral particles (virions) are generally enveloped (external enveloped virion), though the
intracellular mature virion ''Poxviridae'' is a family of double-stranded DNA viruses. Vertebrates and arthropods serve as natural hosts. There are currently 83 species in this family, divided among 22 genera, which are divided into two subfamilies. Diseases associated wit ...
form of the virus, which contains different envelope, is also infectious. They vary in their shape depending upon the species but are generally shaped like a brick or as an oval form similar to a rounded brick because they are wrapped by the endoplasmic reticulum. The virion is exceptionally large, its size is around 200 nm in diameter and 300 nm in length and carries its
genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding gen ...
in a single, linear, double-stranded segment of DNA. By comparison,
rhinovirus The rhinovirus (from the grc, ῥίς, rhis "nose", , romanized: "of the nose", and the la, vīrus) is the most common viral infectious agent in humans and is the predominant cause of the common cold. Rhinovirus infection proliferates in tem ...
es are 1/10 as large as a typical ''Poxviridae'' virion.


Genome

Phylogenetic analysis of 26 different chordopoxvirus genomes has shown that the central region of the genome is conserved and contains ~90 genes. The termini in contrast are not conserved between species. Of this group Avipoxvirus is the most divergent. The next most divergent is Molluscipoxvirus. Capripoxvirus, Leporipoxvirus, Suipoxvirus and Yatapoxvirus genera cluster together: Capripoxvirus and Suipoxvirus share a common ancestor and are distinct from the genus Orthopoxvirus. Within the Othopoxvirus genus Cowpox virus strain Brighton Red, Ectromelia virus and Monkeypox virus do not group closely with any other member.
Variola virus Smallpox was an infectious disease caused by variola virus (often called smallpox virus) which belongs to the genus Orthopoxvirus. The last naturally occurring case was diagnosed in October 1977, and the World Health Organization (WHO) cer ...
and
Camelpox virus Camelpox is a disease of camels caused by the camelpox virus (CMPV) of the family ''Poxviridae'', subfamily ''Chordopoxvirinae'', and the genus ''Orthopoxvirus''. It causes skin lesions and a generalized infection. Approximately 25% of young ca ...
form a subgroup. Vaccinia virus is most closely related to CPV-GRI-90. The
GC-content In molecular biology and genetics, GC-content (or guanine-cytosine content) is the percentage of nitrogenous bases in a DNA or RNA molecule that are either guanine (G) or cytosine (C). This measure indicates the proportion of G and C bases out o ...
of family member genomes differ considerably. 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.


Replication

Replication of the poxvirus involves several stages. The virus first binds to a receptor on the host cell surface; the receptors for the poxvirus are thought to be
glycosaminoglycan Glycosaminoglycans (GAGs) or mucopolysaccharides are long, linear polysaccharides consisting of repeating disaccharide units (i.e. two-sugar units). The repeating two-sugar unit consists of a uronic sugar and an amino sugar, except in the case ...
s. After binding to the receptor, the virus enters the cell where it uncoats. Uncoating of the virus is a two step process. 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. The pox viral genes are expressed in two phases. 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. The late genes are expressed after the genome has been replicated and encode the structural proteins to make the virus particle. The assembly of the virus particle occurs in five stages of maturation that lead to the final exocytosis of the new enveloped virion. After the genome has been replicated, the immature virion assembles the A5 protein to create the intracellular mature virion. The protein aligns and the brick-shaped envelope of the intracellular enveloped virion. 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. 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. 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. The replication of poxvirus is unusual for a virus with double-stranded DNA genome because it occurs in the cytoplasm,. although this is typical of other large DNA viruses. Poxvirus encodes its own machinery for genome transcription, a DNA dependent RNA polymerase, 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 Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucle ...
, and therefore most double-stranded DNA viruses carry out a part of their infection cycle within the host cell's nucleus.


Evolution

The ancestor of the poxviruses is not known but structural studies suggest it may have been an
adenovirus Adenoviruses (members of the family ''Adenoviridae'') are medium-sized (90–100 nm), nonenveloped (without an outer lipid bilayer) viruses with an icosahedral nucleocapsid containing a double-stranded DNA genome. Their name derives from thei ...
or a species related to both the poxviruses and the adenoviruses. Based on the genome organisation and DNA replication mechanism a phylogenetic relationships may exist between the rudiviruses (''
Rudiviridae ''Rudiviridae'' is a family of viruses with linear double stranded DNA genomes that infect archaea. The viruses of this family are highly thermostable and can act as a template for site-selective and spatially controlled chemical modification. Fu ...
'') and the large eukaryal DNA viruses: the African swine fever virus ('' Asfarviridae''), Chlorella viruses (''
Phycodnaviridae ''Phycodnaviridae'' is a family of large (100–560 kb) double-stranded DNA viruses that infect marine or freshwater eukaryotic algae. Viruses within this family have a similar morphology, with an icosahedral capsid (polyhedron with 20 fac ...
'') and poxviruses (''Poxviridae''). The mutation rate in poxvirus genomes has been estimated to be 0.9–1.2 x 10−6 substitutions per site per year.Babkin IV, Shchelkunov SN (2006) The time scale in poxvirus evolution. Mol Biol (Mosk) 40(1):20-24 A second estimate puts this rate at 0.5–7 × 10−6 nucleotide substitutions per site per year. A third estimate places the rate at 4–6 × 10−6. The last common ancestor of the extant poxviruses that infect vertebrates existed . 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 . A second estimate of this divergence time places this event at 166,000 ± 43,000 years ago. 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. An isolate from a fish – salmon gill poxvirus – appears to be the earliest branch in the ''Chordopoxvirinae''. A new systematic has been proposed recently after findings of a new squirrel poxvirus in Berlin, Germany.


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. 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. A second estimate has placed the separation of variola from Taterapox at 3000–4000 years ago. This is consistent with archaeological and historical evidence regarding the appearance of smallpox as a human disease which suggests a relatively recent origin. However, if the mutation rate is assumed to be similar to that of the
herpesvirus ''Herpesviridae'' is a large family of DNA viruses that cause infections and certain diseases in animals, including humans. The members of this family are also known as herpesviruses. The family name is derived from the Greek word ''ἕρπει� ...
es the divergence date between variola from Taterapox has been estimated to be 50,000 years ago. While this is consistent with the other published estimates it suggests that the archaeological and historical evidence is very incomplete. Better estimates of mutation rates in these viruses are needed.


Taxonomy

The species in the subfamily ''
Chordopoxvirinae ''Chordopoxvirinae'' is a subfamily of viruses in the family ''Poxviridae''. Humans, vertebrates, and arthropods serve as natural hosts. Currently, 52 species are placed in this subfamily, divided among 18 genera. Diseases associated with this s ...
'' infect
vertebrate Vertebrates () comprise all animal taxon, taxa within the subphylum Vertebrata () (chordates with vertebral column, backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the ...
s and those in the subfamily ''
Entomopoxvirinae ''Entomopoxvirinae'' is a subfamily of viruses, in the family ''Poxviridae''. Insects, human, vertebrates, and arthropods serve as natural hosts. There are currently 31 species in this subfamily, divided among 4 genera with one species unassign ...
'' infect
insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs of ...
s. 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): ''
Chordopoxvirinae ''Chordopoxvirinae'' is a subfamily of viruses in the family ''Poxviridae''. Humans, vertebrates, and arthropods serve as natural hosts. Currently, 52 species are placed in this subfamily, divided among 18 genera. Diseases associated with this s ...
'' * ''
Avipoxvirus ''Avipoxvirus'' (avian pox) is a genus of viruses within the family ''Poxviridae''. ''Poxviridae'' is the family of viruses which cause the afflicted organism to have poxes as a symptom. Poxviruses have generally large genomes, and other such ex ...
'' * ''
Capripoxvirus ''Capripoxvirus'' is a genus of viruses in the subfamily ''Chordopoxvirinae'' and the family ''Poxviridae''. Capripoxviruses are among the most serious of all animal poxviruses. All CaPV are notifiable disease A notifiable disease is any disea ...
'' * ''Centapoxvirus'' * ''
Cervidpoxvirus ''Cervidpoxvirus'' is a genus of viruses in the family ''Poxviridae'' in the subfamily ''Chordopoxvirinae ''Chordopoxvirinae'' is a subfamily of viruses in the family ''Poxviridae''. Humans, vertebrates, and arthropods serve as natural hosts ...
'' * ''
Crocodylidpoxvirus ''Crocodylidpoxvirus'' is a genus of viruses, in the family ''Poxviridae'', in the subfamily ''Chordopoxvirinae ''Chordopoxvirinae'' is a subfamily of viruses in the family ''Poxviridae''. Humans, vertebrates, and arthropods serve as natural ...
'' * ''
Leporipoxvirus ''Leporipoxvirus'' is a genus of viruses, in the family ''Poxviridae'', in the subfamily ''Chordopoxvirinae''. Lagomorphs and squirrels serve as natural hosts. There are four species in this genus. Diseases associated with this genus include: ...
'' * ''Macropopoxvirus'' * ''
Molluscipoxvirus ''Molluscum contagiosum virus'' (MCV) is a species of DNA poxvirus that causes the human skin infection molluscum contagiosum. Molluscum contagiosum affects about 200,000 people a year, about 1% of all diagnosed skin diseases. Diagnosis is base ...
'' * ''Mustelpoxvirus'' * ''
Orthopoxvirus ''Orthopoxvirus'' is a genus of viruses in the family ''Poxviridae'' and subfamily ''Chordopoxvirinae''. Vertebrates, including mammals and humans, and arthropods serve as natural hosts. There are 12 species in this genus. Diseases associated wi ...
'' * ''Oryzopoxvirus'' * ''
Parapoxvirus ''Parapoxvirus'' is a genus of viruses, in the family ''Poxviridae'', in the subfamily ''Chordopoxvirinae''. Like all members of the family Poxviridae, they are oval, relatively large, double-stranded DNA viruses. Parapoxviruses have a unique sp ...
'' * ''Pteropopoxvirus'' * ''Salmonpoxvirus'' * ''Sciuripoxvirus'' * ''
Suipoxvirus ''Suipoxvirus'' is a genus of viruses in the family ''Poxviridae'' and subfamily ''Chordopoxvirinae''. Swine serve as natural hosts. There is only one species in this genus: ''Swinepox virus''. Diseases associated with this genus include asympto ...
'' * ''Vespertilionpoxvirus'' * ''
Yatapoxvirus ''Yatapoxvirus'' is a genus of viruses, in the family ''Poxviridae'', in the subfamily ''Chordopoxvirinae''. Monkeys and baboons serve as natural hosts. There are two species in this genus. Diseases associated with this genus include: histiocyto ...
'' ''
Entomopoxvirinae ''Entomopoxvirinae'' is a subfamily of viruses, in the family ''Poxviridae''. Insects, human, vertebrates, and arthropods serve as natural hosts. There are currently 31 species in this subfamily, divided among 4 genera with one species unassign ...
'' * '' Alphaentomopoxvirus'' * ''
Betaentomopoxvirus ''Betaentomopoxvirus'' is a genus of viruses, in the family ''Poxviridae ''Poxviridae'' is a family of double-stranded DNA viruses. Vertebrates and arthropods serve as natural hosts. There are currently 83 species in this family, divided ...
'' * ''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.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 Cotia virus was assigned the new genus '' Oryzopoxvirus'' in 2019. A Brazilian porcupinepox virus discovered in 2019 is closely related to the virus. * Two more chordopoxviruses are NY_014 and murmansk poxvirus. They are considered closely related to a "Yoka poxvirus".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 ICTV classifies them under a genus '' Centapoxvirus'', created 2016.


Vaccinia virus

The prototypical poxvirus is
vaccinia virus ''Vaccinia virus'' (VACV or VV) is a large, complex, enveloped virus belonging to the poxvirus family. It has a linear, double-stranded DNA genome approximately 190 kbp in length, which encodes approximately 250 genes. The dimensions of the v ...
, known for its role in the eradication of smallpox. The vaccinia virus is an effective tool for foreign protein expression, as it elicits a strong host immune-response. The vaccinia virus enters cells primarily by cell fusion, although currently the receptor responsible is unknown. 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.


See also

* Quokkapox virus * Water warts


References


External links

*
Electron micrograph A micrograph or photomicrograph is a photograph or digital image taken through a microscope or similar device to show a magnify, magnified image of an object. This is opposed to a macrograph or photomacrograph, an image which is also taken ...
s of ''Orthopoxvirus'' and ''Parapoxvirus''
Genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomencl ...
, including the
smallpox Smallpox was an infectious disease caused by variola virus (often called smallpox virus) which belongs to the genus Orthopoxvirus. The last naturally occurring case was diagnosed in October 1977, and the World Health Organization (WHO) cer ...
virus, have been collected by the
International Committee on Taxonomy of Viruses The International Committee on Taxonomy of Viruses (ICTV) authorizes and organizes the taxonomic classification of and the nomenclatures for viruses. The ICTV has developed a universal taxonomic scheme for viruses, and thus has the means to app ...
in thei
''Poxviridae'' picture gallery
*
NCBI Taxonomy Page

Poxviridae at the Viral Bioinformatics Resource Center



ICTV

Virus Pathogen Database and Analysis Resource (ViPR): Poxviridae
{{Taxonbar, from=Q948421 Virus families