| Herpesvirales | |
|---|---|
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| Simplified diagram ofHerpesvirales virion structure in cross-section. (1) nucleoprotein, (2) DNA, (3) capsid, (4) tegument, (5) envelope, (6) glycoprotein. Click to enlarge. | |
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| Electron micrograph of various viruses from theOrthoherpesviridae family includingHuman alphaherpesvirus 3 (Chickenpox),Human alphaherpesvirus 1, andHuman alphaherpesvirus 2 | |
Virus classification | |
| (unranked): | Virus |
| Realm: | Duplodnaviria |
| Kingdom: | Heunggongvirae |
| Phylum: | Peploviricota |
| Class: | Herviviricetes |
| Order: | Herpesvirales |
| Families | |
Herpesvirales is an order of dsDNAviruses (Baltimore group I) with animal hosts, characterised by a common morphology consisting of anicosahedralcapsid enclosed in a glycoprotein-containing lipid envelope. Common infections in humans caused by members of this order includecold sores,genital herpes,chickenpox,shingles, andglandular fever.Herpesvirales is the sole order in the classHerviviricetes, which is the sole class in the phylumPeploviricota.
All members of the order have a virion structure that consists of a DNA core surrounded by an icosahedral capsid composed of 12 pentavalent and 150 hexavalentcapsomeres (T = 16). The capsid has a diameter of ~110 nanometers (nm) and is embedded in a proteinaceous matrix called thetegument, which in its turn is enclosed by a glycoprotein-containing lipid envelope with a diameter of about 200 nm. The DNA genome is linear and double stranded, with sizes in the range 125–290 kbp.[1] The genome contains terminal and internal reiterated sequences, with their number and disposition varying depending on the different subclades.
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All species in this order have animal hosts. TheMalacoherpesviridae infect molluscs (abalone and oysters), theAlloherpesviridae infectanamniotes (frogs and fish), and theHerpesviridae infectamniotes (reptiles, birds, and mammals). Within the familyHerpesviridae, generaIltovirus andMardivirus, and genusScutavirus of the subfamilyAlphaherpesvirinae infect birds and reptiles, respectively. All other genera in theHerpesviridae infect mammals only.[2]
Herpesvirales contains three families:[3]
Theherpesvirus was first isolated from theblue wildebeest in 1960 by veterinary scientistWalter Plowright.[4] The genusHerpesvirus was established in 1971 in the first report of theInternational Committee on Taxonomy of Viruses (ICTV). This genus consisted of 23 viruses and 4 groups of viruses. In the second ICTV report in 1976 this genus was elevated to family level - theHerpetoviridae. Because of possible confusion with viruses derived fromreptiles this name was changed in the third report in 1979 toHerpesviridae. In this report the familyHerpesviridae was divided into 3 subfamilies (Alphaherpesvirinae,Betaherpesvirinae andGammaherpesvirinae) and 5 unnamed genera: 21 viruses were listed. In 2009 the familyHerpesviridae was elevated to the orderHerpesvirales. This elevation was necessitated by the discovery that the herpesviruses offish andmolluscs were only distantly related to those ofbirds andmammals.[5] Two new families were created - the familyAlloherpesviridae which incorporates bony fish and frog viruses and the familyMalacoherpesviridae which contains those of molluscs.
The only protein with widespread conservation amongst all members of the order, albeit only at the amino-acid level, is the ATPase subunit of the DNA terminase;[1] the latter is involved in the packaging of the DNA during virion assembly.[6]
Phylogenies constructed with the conserved regions of the ATPase subunit of the DNA terminase suggest thatAlloherpesviridae is the basalclade of the order, and thatHerpesviridae andMalacoherpesviridae are sister clades.[7] Given the phylogenetic distances between vertebrates and molluscs, this suggests that herpesviruses were initially fish viruses and that they have evolved with their hosts to infect other vertebrates.[citation needed]
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