Herpesviridae#Human herpesvirus types

The family has the following subfamilies and genera:

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• Subfamily Alphaherpesvirinae
• Iltovirus
• Mardivirus
• Scutavirus
• Simplexvirus
• Varicellovirus
• Subfamily Betaherpesvirinae
• Cytomegalovirus
• Muromegalovirus
• Proboscivirus
• Quwivirus
• Roseolovirus
• Subfamily Gammaherpesvirinae
• Bossavirus
• Lymphocryptovirus
• Macavirus
• Manticavirus
• Patagivirus
• Percavirus
• Rhadinovirus

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A number of other herpesviruses were previously recognized as species but were abolished, so their exact taxonomic placement is uncertain. These viruses include: Chelonid alphaherpesvirus 6, Cercopithecine gammaherpesvirus 14, Equid gammaherpesvirus 7, Iguanid herpesvirus 2, Phocid gammaherpesvirus 2, and Saguinine gammaherpesvirus 1.{{cite web|vauthors=Benkő M, Brandt CR, Bryant NA, Dastjerdi A, Davison AJ, Depledge DP, Doszpoly A, Gatherer D, Gompels UA, Hartley CA, Inoue N, Jarosinski KW, Kaul R, Lacoste V, Norberg P, Origgi FC, Orton RJ, Pellett PE, Schmid DS, Spatz SJ, Stewart JP, Szpara ML, Trimpert J, Vaz P, Waltzek TB|title=Abolish 6 species and rename 1 family, 4 genera and 124 species in the order Herpesvirales|url=https://ictv.global/ictv/proposals/2022.001D.Herpesvirales_1renfam_4rengen_124rensp_6absp.zip|website=ictv.global|publisher=International Committee on Taxonomy of Viruses|date=20 May 2022|access-date=2 February 2025|format=docx}}

File:Herpesviridae virion.jpg

All members of the Herpesviridae share a common structure; a relatively large, monopartite, double-stranded, linear DNA genome encoding 100–200 genes encased within an icosahedral protein cage (with T=16 symmetry) called the capsid, which is itself wrapped in a protein layer called the tegument containing both viral proteins and viral mRNAs and a lipid bilayer membrane called the envelope. This whole particle is known as a virion.

The structural components of a typical HSV virion are the Lipid bilayer envelope, Tegument, DNA, Glycoprotein spikes and Nucleocapsid. The four-component Herpes simplex virion encompasses the double-stranded DNA genome into an icosahedral nucleocapsid. There is tegument around. Tegument contains filaments, each 7 nm wide. It is an amorphous layer with some structured regions. Finally, it is covered with a lipoprotein envelope. There are spikes made of glycoprotein protruding from each virion. These can expand the diameter of the virus to 225 nm. The diameters of virions without spikes are around 186 nm. There are at least two unglycosylated membrane proteins in the outer envelope of the virion. There are also 11 glycoproteins. These are gB, gC, gD, gE, gG, gH, gI, gJ, gK, gL and gM. Tegument contains 26 proteins. They have duties such as capsid transport to the nucleus and other organelles, activation of early gene transcription, and mRNA degradation. The icosahedral nucleocapsid is similar to that of tailed bacteriophage in the order Caudovirales. This capsid has 161 capsomers consisting of 150 hexons and 11 pentons, as well as a portal complex that allows entry and exit of DNA into the capsid.Liu, Y., Jih, J., Dai, X. et al. Cryo-EM structures of herpes simplex virus type 1 portal vertex and packaged genome. Nature 570, 257–261 (2019). https://doi.org/10.1038/s41586-019-1248-6Das, D., & Hong, J. (2019). Herpesvirus Polymerase Inhibitors. In Viral Polymerases (pp. 333–356). Elsevier. https://doi.org/10.1016/B978-0-12-815422-9.00012-7

All herpesviruses are nuclear-replicating—the viral DNA is transcribed to mRNA within the infected cell's nucleus.{{citation needed|date=September 2022}}

Infection is initiated when a viral particle contacts a cell with specific types of receptor molecules on the cell surface. Following binding of viral envelope glycoproteins to cell membrane receptors, the virion is internalized and dismantled, allowing viral DNA to migrate to the cell nucleus. Within the nucleus, replication of viral DNA and transcription of viral genes occurs.{{citation needed|date=September 2022}}

During symptomatic infection, infected cells transcribe lytic viral genes. In some host cells, a small number of viral genes termed latency-associated transcript (LAT) accumulate, instead. In this fashion, the virus can persist in the cell (and thus the host) indefinitely. While primary infection is often accompanied by a self-limited period of clinical illness, long-term latency is symptom-free.{{citation needed|date=September 2022}}

Chromatin dynamics regulate the transcription competency of entire herpes virus genomes. When the virus enters a cell, the cellular immune response is to protect the cell. The cell does so by wrapping the viral DNA around histones and condensing it into chromatin, causing the virus to become dormant, or latent. If cells are unsuccessful and the chromatin is loosely bundled, the viral DNA is still accessible. The viral particles can turn on their genes and replicate using cellular machinery to reactivate, starting a lytic infection.{{cite journal | vauthors = Hu M, Depledge DP, Flores Cortes E, Breuer J, Schang LM | title = Chromatin dynamics and the transcriptional competence of HSV-1 genomes during lytic infections | journal = PLOS Pathogens | volume = 15 | issue = 11 | pages = e1008076 | date = November 2019 | pmid = 31725813 | pmc = 6855408 | doi = 10.1371/journal.ppat.1008076 | doi-access = free }}

Reactivation of latent viruses has been implicated in a number of diseases (e.g. shingles, pityriasis rosea). Following activation, transcription of viral genes transitions from LAT to multiple lytic genes; these lead to enhanced replication and virus production. Often, lytic activation leads to cell death. Clinically, lytic activation is often accompanied by emergence of nonspecific symptoms, such as low-grade fever, headache, sore throat, malaise, and rash, as well as clinical signs such as swollen or tender lymph nodes and immunological findings such as reduced levels of natural killer cells.{{citation needed|date=September 2022}}

In animal models, local trauma and system stress have been found to induce reactivation of latent herpesvirus infection. Cellular stressors like transient interruption of protein synthesis and hypoxia are also sufficient to induce viral reactivation.{{cite journal | vauthors = Grinde B | title = Herpesviruses: latency and reactivation – viral strategies and host response | journal = Journal of Oral Microbiology | volume = 5 | issue = 1 | pages = 22766 | date = October 2013 | pmid = 24167660 | pmc = 3809354 | doi = 10.3402/jom.v5i0.22766 }}

The three mammalian subfamilies – Alpha-, Beta- and Gamma-herpesviridae – arose approximately 180 to 220 mya.{{cite journal | vauthors = McGeoch DJ, Cook S, Dolan A, Jamieson FE, Telford EA | title = Molecular phylogeny and evolutionary timescale for the family of mammalian herpesviruses | journal = Journal of Molecular Biology | volume = 247 | issue = 3 | pages = 443–58 | date = March 1995 | pmid = 7714900 | doi = 10.1006/jmbi.1995.0152 }} The major sublineages within these subfamilies were probably generated before the mammalian radiation of 80 to 60 mya. Speciations within sublineages took place in the last 80 million years probably with a major component of cospeciation with host lineages.{{citation needed|date=September 2022}}

All the currently known bird and reptile species are alphaherpesviruses. Although the branching order of the herpes viruses has not yet been resolved, because herpes viruses and their hosts tend to coevolve this is suggestive that the alphaherpesviruses may have been the earliest branch.{{citation needed|date=September 2022}}

The time of origin of the genus Iltovirus has been estimated to be 200 mya while those of the mardivirus and simplex genera have been estimated to be between 150 and 100 mya.{{cite journal | vauthors = McGeoch DJ, Rixon FJ, Davison AJ | title = Topics in herpesvirus genomics and evolution | journal = Virus Research | volume = 117 | issue = 1 | pages = 90–104 | date = April 2006 | pmid = 16490275 | doi = 10.1016/j.virusres.2006.01.002 }}

{{missing information|section|latency mechanisms beyond CMV, e.g. HSV LAT and ICP-47; whether there is a common mechanism in the family|date=November 2021}}

Herpesviruses are known for their ability to establish lifelong infections. One way this is possible is through immune evasion. Herpesviruses have many different ways of evading the immune system. One such way is by encoding a protein mimicking human interleukin 10 (hIL-10) and another is by downregulation of the major histocompatibility complex II (MHC II) in infected cells.

Research conducted on cytomegalovirus (CMV) indicates that the viral human IL-10 homolog, cmvIL-10, is important in inhibiting pro-inflammatory cytokine synthesis. The cmvIL-10 protein has 27% identity with hIL-10 and only one conserved residue out of the nine amino acids that make up the functional site for cytokine synthesis inhibition on hIL-10. There is, however, much similarity in the functions of hIL-10 and cmvIL-10. Both have been shown to down regulate IFN-γ, IL-1α, GM-CSF, IL-6 and TNF-α, which are all pro-inflammatory cytokines. They have also been shown to play a role in downregulating MHC I and MHC II and up regulating HLA-G (non-classical MHC I). These two events allow for immune evasion by suppressing the cell-mediated immune response and natural killer cell response, respectively. The similarities between hIL-10 and cmvIL-10 may be explained by the fact that hIL-10 and cmvIL-10 both use the same cell surface receptor, the hIL-10 receptor. One difference in the function of hIL-10 and cmvIL-10 is that hIL-10 causes human peripheral blood mononuclear cells (PBMC) to both increase and decrease in proliferation whereas cmvIL-10 only causes a decrease in proliferation of PBMCs. This indicates that cmvIL-10 may lack the stimulatory effects that hIL-10 has on these cells.{{cite journal | vauthors = Spencer JV, Lockridge KM, Barry PA, Lin G, Tsang M, Penfold ME, Schall TJ | title = Potent immunosuppressive activities of cytomegalovirus-encoded interleukin-10 | journal = Journal of Virology | volume = 76 | issue = 3 | pages = 1285–92 | date = February 2002 | pmid = 11773404 | pmc = 135865 | doi = 10.1128/JVI.76.3.1285-1292.2002 }}

It was found that cmvIL-10 functions through phosphorylation of the Stat3 protein. It was originally thought that this phosphorylation was a result of the JAK-STAT pathway. However, despite evidence that JAK does indeed phosphorylate Stat3, its inhibition has no significant influence on cytokine synthesis inhibition. Another protein, PI3K, was also found to phosphorylate Stat3. PI3K inhibition, unlike JAK inhibition, did have a significant impact on cytokine synthesis. The difference between PI3K and JAK in Stat3 phosphorylation is that PI3K phosphorylates Stat3 on the S727 residue whereas JAK phosphorylates Stat3 on the Y705 residue. This difference in phosphorylation positions seems to be the key factor in Stat3 activation leading to inhibition of pro-inflammatory cytokine synthesis. In fact, when a PI3K inhibitor is added to cells, the cytokine synthesis levels are significantly restored. The fact that cytokine levels are not completely restored indicates there is another pathway activated by cmvIL-10 that is inhibiting cytokine system synthesis. The proposed mechanism is that cmvIL-10 activates PI3K which in turn activates PKB (Akt). PKB may then activate mTOR, which may target Stat3 for phosphorylation on the S727 residue.{{cite journal | vauthors = Spencer JV | title = The cytomegalovirus homolog of interleukin-10 requires phosphatidylinositol 3-kinase activity for inhibition of cytokine synthesis in monocytes | journal = Journal of Virology | volume = 81 | issue = 4 | pages = 2083–6 | date = February 2007 | pmid = 17121792 | pmc = 1797587 | doi = 10.1128/JVI.01655-06 | url = http://repository.usfca.edu/cgi/viewcontent.cgi?article=1015&context=biol_fac }}

Another one of the many ways in which herpes viruses evade the immune system is by down regulation of MHC I and MHC II. This is observed in almost every human herpesvirus. Down regulation of MHC I and MHC II can come about by many different mechanisms, most causing the MHC to be absent from the cell surface. As discussed above, one way is by a viral chemokine homolog such as IL-10. Another mechanism to down regulate MHCs is to encode viral proteins that detain the newly formed MHC in the endoplasmic reticulum (ER). The MHC cannot reach the cell surface and therefore cannot activate the T cell response. The MHCs can also be targeted for destruction in the proteasome or lysosome. The ER protein TAP also plays a role in MHC down regulation. Viral proteins inhibit TAP preventing the MHC from picking up a viral antigen peptide. This prevents proper folding of the MHC and therefore the MHC does not reach the cell surface.{{cite journal | vauthors = Lin A, Xu H, Yan W | title = Modulation of HLA expression in human cytomegalovirus immune evasion | journal = Cellular & Molecular Immunology | volume = 4 | issue = 2 | pages = 91–8 | date = April 2007 | pmid = 17484802 }}

Below are the nine distinct viruses in this family known to cause disease in humans.{{cite journal | vauthors = Adams MJ, Carstens EB | title = Ratification vote on taxonomic proposals to the International Committee on Taxonomy of Viruses (2012) | journal = Archives of Virology | volume = 157 | issue = 7 | pages = 1411–22 | date = July 2012 | pmid = 22481600 | doi = 10.1007/s00705-012-1299-6 | pmc = 7086667 | doi-access = free }}{{cite book | author = Whitley RJ | title = Herpesviruses. in: Baron's Medical Microbiology| editor = Baron S| display-editors = etal| edition = 4th | publisher = Univ of Texas Medical Branch | year = 1996 | url = https://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed.chapter.3567 | isbn = 0-9631172-1-1 }}{{cite book |vauthors=Murray PR, Rosenthal KS, Pfaller MA | title = Medical Microbiology | edition = 5th | publisher = Elsevier Mosby | year = 2005 | isbn = 978-0-323-03303-9 }}

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In addition to the herpesviruses considered endemic in humans, some viruses associated primarily with animals may infect humans. These are zoonotic infections:

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In animal virology, the best known herpesviruses belong to the subfamily Alphaherpesvirinae. Research on pseudorabies virus (PrV), the causative agent of Aujeszky's disease in pigs, has pioneered animal disease control with genetically modified vaccines. PrV is now extensively studied as a model for basic processes during lytic herpesvirus infection, and for unraveling molecular mechanisms of herpesvirus neurotropism, whereas bovine herpesvirus 1, the causative agent of bovine infectious rhinotracheitis and pustular vulvovaginitis, is analyzed to elucidate molecular mechanisms of latency. The avian infectious laryngotracheitis virus is phylogenetically distant from these two viruses and serves to underline similarity and diversity within the Alphaherpesvirinae.

{{Main|Herpes simplex research}}

Research is currently ongoing into a variety of side-effect or co-conditions related to the herpesviruses. These include:{{citation needed|date=December 2024}}

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• Alzheimer's disease
• atherosclerosis
• cholangiocarcinoma
• chronic fatigue syndrome
• Crohn's disease{{citation needed|date=December 2024}}
• dysautonomia
• fibromyalgia
• Irritable bowel syndrome{{citation needed|date=December 2024}}
• labile hypertension
• lupus
• Ménière's disease
• multiple sclerosis
• pancreatic cancer
• pancreatitis
• pityriasis rosea
• Type II Diabetes

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• Acciptrid herpesvirus 1
• Agua Preta virus, a potential herpesvirus

{{Reflist|30em}}

{{Wikispecies|Herpesviridae}}

{{Commons category|Herpesviridae}}

• [https://web.archive.org/web/20150120190449/http://www.ictvonline.org/index.asp?bhcp=1 ICTV International Committee on Taxonomy of Viruses (official site)]
• [http://www.expasy.org/viralzone/all_by_species/176.html Viralzone: Herpesviridae]
• [http://www.horizonpress.com/gateway/animal-viruses.html Animal viruses]
• [https://www.cdc.gov/ncidod/diseases/bvirus.pdf Article on Cercopithecine herpesvirus]
• [http://www.gsu.edu/bvirus National B Virus Resource Center]
• [http://www.aocd.org/skin/dermatologic_diseases/pityriasis_rosea.html Pityriasis Rosea overview]
• [https://www.wikigenes.org/e/art/e/61.html Herpes simplex: Host viral protein interactions.A database of Host/HSV-1 interactions] {{Webarchive|url=https://web.archive.org/web/20100812033023/https://www.wikigenes.org/e/art/e/61.html |date=12 August 2010 }}
• [http://www.viprbrc.org/brc/home.do?decorator=herpes Virus Pathogen Database and Analysis Resource (ViPR): Herpesviridae]

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