Human betaherpesvirus 7

Human betaherpesvirus 7 (HHV-7) is one of nine known members of the Herpesviridae family that infects humans. HHV-7 is a member of Betaherpesvirinae, a subfamily of the Herpesviridae that also includes HHV-6 and Cytomegalovirus (HHV-5 or HCMV).[2][3] HHV-7 often acts together with HHV-6, and the viruses together are sometimes referred to by their genus, Roseolovirus.[4] HHV-7 was first isolated in 1990 from CD4+ T cells taken from peripheral blood lymphocytes.[5]

Human betaherpesvirus 7
SpecialtyInfectious disease
Human betaherpesvirus 7
Virus classification
(unranked): Virus
Realm: Duplodnaviria
Kingdom: Heunggongvirae
Phylum: Peploviricota
Class: Herviviricetes
Order: Herpesvirales
Family: Herpesviridae
Genus: Roseolovirus
Species:
Human betaherpesvirus 7
Synonyms[1]
  • Human herpesvirus 7

Signs and symptoms

Both HHV-6B and HHV-7, as well as other viruses, can cause a skin condition in infants known as exanthema subitum, although HHV-7 causes the disease less frequently than HHV-6B.[6] HHV-7 infection also leads to or is associated with a number of other symptoms, including acute febrile respiratory disease, fever, rash, vomiting, diarrhea, low lymphocyte counts,[7] and febrile seizures,[8] though most often no symptoms present at all.[9]

There are indications that HHV-7 can contribute to the development of drug-induced hypersensitivity syndrome,[10] encephalopathy,[11] hemiconvulsion-hemiplegia-epilepsy syndrome,[12] hepatitis infection,[13] postinfectious myeloradiculoneuropathy,[14] pityriasis rosea,[15] and the reactivation of HHV-4, leading to "mononucleosis-like illness".[16]

Complications with HHV-7 infection has been shown to be a factor in a great variety of transplant types.[9]

Virology

Structure

A mature virus particle measures about 170 nanometres (1,700 Å) in diameter.[17]

The genome of HHV-7 is very similar to that of HHV-6, although it is about 10% smaller,[18] with a DNA genome of about 145,000 base pairs.[9] There are a number of key differences between the genome of HHV-7 and that of HHV-6, but the importance of them for viral DNA replication is not yet known.[9]

Cellular effects

HHV-7 resides mostly in CD4+ T cells,[19] albeit only in certain strains of them.[20][21][22] To enter CD4+ T cells, HHV-7, unlike HHV-6, uses CD4 and possibly some cell-surface glyoproteins to enter CD4+ T cells.[23] About a week after HHV-7 has infected a cell, it begins to downregulate CD4 transcription,[24] which interferes with HIV-1 infection[25] but may reactivate HHV-6 infection.[26] It is however unclear exactly what effect HHV-7 has on HIV infection.[9]

HHV-7 also has a number of other effects on cells. Among these include membrane leaking, the presence of lytic syncytia,[27][28] occasional apoptosis,[29] the supporting of latent infection,[30] and increases and decreases in levels of certain cytokines.[31][32]

Detection and treatment

In adults, the effects of HHV-7 separate from HHV-6 have not been well-researched.[2] One reason for this is because the detection of HHV-7 was at first difficult to do quickly, as the process for doing so involves a procedure that is difficult to do in commercial laboratories and because viral isolation and serological testing are long processes that do not lend themselves to finishing quickly. A process known as loop-mediated isothermal amplification (LAMP) has recently been developed to speed up detection of HHV-7, although a larger sample size of patients must be tested first to see if the test will still work across a broad range of subjects.[33] No reliable serological test has been developed yet for HHV-7 alone, but multiple are in the process of being developed.[9] The use of PCR assays to test for HHV-7 is also being explored.[9][34]

No treatment for HHV-7 infection exists, but no clinical situation where such treatment would be useful has yet been discovered.[9]

Epidemiology

Over 95% of adults have been infected and are immune to HHV-7,[35] and over three quarters of those were infected before the age of six.[36] Primary infection of HHV-7 among children generally occurs between the ages of 2 and 5, which means it occurs after primary infection of HHV-6.[37] A 2014 Washington University School of Medicine's analysis of 102 healthy adults sampled at as many as five major body habitats found that HHV-7 was present in 98% of them, especially in the mouth.[38] A 2017 study looking at the human blood virome in 8,240 humans between the ages of 2 months to 102 years found that 20.37% of them were positive for HHV-7.[39]

References
  1. Davison, Andrew (27 January 2016). "Rename species in the family Herpesviridae to incorporate a subfamily designation" (PDF). International Committee on Taxonomy of Viruses (ICTV). Retrieved 13 March 2019.
  2. "Other Herpesviruses: HHV-6, HHV-7, HHV-8, HSV-1 and -2, VZV". American Journal of Transplantation. 4 Suppl 10: 66–71. 2004. doi:10.1111/j.1600-6135.2004.00697.x. PMID 15504215.
  3. Widen, B. F.; Lowings, J. P.; Belak, S.; Banks, M. (August 1999). "Development of a PCR system for porcine cytomegalovirus detection and determination of the putative partial sequence of its DNA polymerase gene". Epidemiology and Infection. 123 (1): 177–180. doi:10.1017/S0950268899002599. PMC 2810741. PMID 10487654.
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Further reading
Wikispecies has information related to Human betaherpesvirus 7.
  • Arvin, Ann; Whitley, Richard (2007). "Part III.4 HHV-6A, 6B, and 7". Human herpesviruses : biology, therapy, and immunoprophylaxis. Cambridge: Cambridge University Press. ISBN 978-0-521-82714-0.
  • Caselli, E; Di Luca, D (2007). "Molecular Biology and Clinical Associations of Roseoloviruses Human Herpesvirus 6 and Human Herpesvirus 7". New Microbiologica. 30 (3): 173–187. PMID 17802896.
  • Dewhurst, S (2004). "Human Herpesvirus Type 6 and Human Herpesvirus Type 7 Infections of the Central Nervous System". Herpes: The Journal of the IHMF. 11 Suppl 2: 105A–111A. PMID 15319097.
  • Kempf, W (2002). "Human Herpesvirus 7 in Dermatology: What Role Does It Play?". American Journal of Clinical Dermatology. 3 (5): 309–315. doi:10.2165/00128071-200203050-00002. PMID 12069636. S2CID 28402208.
  • De Araujo, T; Berman, B; Weinstein, A (2002). "Human Herpesviruses 6 and 7". Dermatologic Clinics. 20 (2): 301–306. doi:10.1016/S0733-8635(01)00008-0. PMID 12120443.
  • Jackson, MA; Sommerauer, JF (2002). "Human Herpesviruses 6 and 7". The Pediatric Infectious Disease Journal. 21 (6): 565–566. doi:10.1097/00006454-200206000-00016. PMID 12182383.
  • Clark, DA (2002). "Human Herpesvirus 6 and Human Herpesvirus 7: Emerging Pathogens in Transplant Patients". International Journal of Hematology. 76 Suppl 2: 246–252. doi:10.1007/bf03165124. PMID 12430932. S2CID 27064788.
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