How is human herpesvirus 6 spread?
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Transmission is believed to occur most frequently through the shedding of viral particles into saliva. Both HHV-6B and HHV-7 are found in human saliva, the former being at a lower frequency. Studies report varying rates of prevalence of HHV-6 in saliva (between 3–90%), and have also described the salivary glands as an in vivo reservoir for HHV-6. The virus infects the salivary glands, establishes latency, and periodically reactivates to spread infection to other hosts.
Human herpesvirus 6
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Human herpesvirus 6 (HHV-6) is the common collective name for human herpesvirus 6A (HHV-6A) and human herpesvirus 6B (HHV-6B). These closely related viruses are two of the nine herpesviruses known to have humans as their primary host.
Human herpesvirus 6
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Human herpesvirus 6 lives primarily on humans and, while variants of the virus can cause mild to fatal illnesses, can live commensally on its host. It has been demonstrated that HHV-6 fosters the progression of HIV-1 upon coinfection in T cells. HHV-6 upregulates the expression of the primary HIV receptor CD4, thus expanding the range of HIV susceptible cells. Several studies also have shown that HHV-6 infection increases production of inflammatory cytokines that enhance in vitro expression of HIV-1, such as TNF-alpha, IL-1 beta, and IL-8. A more recent in vivo study shows HHV-6A coinfection to dramatically accelerate the progression from HIV to AIDS in pigtailed macaques.
Human herpesvirus 6
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Human herpesvirus 7 (HHV-7) is one of nine known members of the Herpesviridae family that infects humans. HHV-7 is a member of Betaherpesviridae, a subfamily of the Herpesviridae that also includes HHV-6 and "cytomegalovirus" (HHV-5 or HCMV). HHV-7 often acts together with HHV-6, and the viruses together are sometimes referred to by their genus, "Roseolovirus". HHV-7 was first isolated in 1990 from CD4+ T cells taken from peripheral blood lymphocytes.
Human herpesvirus 7
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When an extracellular HHV-6 virion comes across human cells, it encounters the human receptor protein cluster of differentiation 46 (CD46), which plays a role in regulating the complement system. The CD46 protein possesses a single variable region, as a result of alternative splicing. As such, at least fourteen isoforms of CD46 exist, all of which bind HHV-6a.
Human herpesvirus 6
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HHV-6 has also been demonstrated to transactivate Epstein–Barr virus.
Human herpesvirus 6
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The role of HHV-6 during pregnancy leading to inflammation in the amniotic cavity has been studied.
Human herpesvirus 6
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The right direct repeat terminus integrates within 5 to 41 human telomere repeats, and preferentially does so into the proximal end of chromosomes 9, 17, 18, 19, and 22, but has also occasionally been found in chromosomes 10 and 11. Nearly 70 million individuals are suspected to carry chromosomally integrated HHV-6.
Human herpesvirus 6
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During maturation of HHV-6 virions, human cell membranes are used to form viral lipid envelopes (as is characteristic of all enveloped viruses). During this process HHV-6 utilizes lipid rafts, which are membranous microdomains enriched by cholesterol, sphingolipids, and glycosylphosphatidylinositol-anchored proteins. Early researchers suspected that HHV-6 virions mature in the nucleus; some even incorrectly published this, as they generalized and applied to HHV-6 what was known about other viruses. However, researched published in 2009 suggests that the HHV-6 virus utilizes trans-Golgi-network-derived vesicles for assembly.
Human herpesvirus 6
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Human cytomegalovirus (HCMV, HHV-5) "seems to have a large impact on immune parameters in later life and may contribute to increased morbidity and eventual mortality." Human herpesvirus 6A (HHV-6A) has been described as more neurovirulent, and as such is more frequently found in patients with neuroinflammatory diseases such as multiple sclerosis. Both human herpesvirus 6B (HHV-6B) and human herpesvirus 7 (HHV-7), as well as other viruses, can cause a skin condition in infants known as exanthema subitum, roseola infantum (rose rash of infants) or the sixth disease.
Betaherpesvirinae