Virology, pathogenesis, and epidemiology of human herpesvirus 6 infection
- Cécile Tremblay, MD
Cécile Tremblay, MD
- Associate Professor
- University of Montreal, Canada
Human herpesvirus 6 (HHV-6) was first isolated and characterized from patients with lymphoproliferative disorders  and was originally named human B-lymphotropic virus. Its name was changed to human herpesvirus 6 as its tropism was further characterized .
The virology, pathogenesis, and epidemiology of HHV-6 infection will be discussed here. The clinical manifestations, diagnosis, and treatment in adults and children are presented separately; HHV-6 infection in hematopoietic cell transplant recipients is also discussed elsewhere. (See "Clinical manifestations, diagnosis, and treatment of human herpesvirus 6 infection in adults" and "Human herpesvirus 6 infection in children: Clinical manifestations; diagnosis; and treatment" and "Human herpesvirus 6 infection in hematopoietic cell transplant recipients".)
Human herpesvirus 6 (HHV-6) is a member of the Herpesviridae family. Its genetic and biologic similarities to human cytomegalovirus (CMV) have prompted its classification in the beta herpesvirus subfamily (genus Roseolovirus, along with human herpesvirus 7 [HHV-7]) . There are two HHV-6 variants, HHV-6A and HHV-6B. Based on their distinctive biological properties and genome sequences, HHV-6A and HHV-6B are classified as two distinct herpesvirus species . HHV-6A and HHV-6B also differ in epidemiology, growth properties, antigenic properties, and restriction endonuclease profiles [5-8]. The nucleotide sequence identity between the two variants ranges from 75 to 95 percent depending upon which gene is compared.
VIROLOGY AND PATHOGENESIS
As with other herpes viruses, mature human herpesvirus 6 (HHV-6) virions are double-stranded DNA viruses, approximately 200 nm in diameter and are composed of four main structural elements: an electron-dense core, a capsid with icosahedral symmetry, a tegument, and an outer envelope.
Cell tropism — HHV-6 replicates most efficiently in vitro in activated primary T cells as well as in continuous T cell lines. However, the virus can also replicate with varying efficiency in a wide array of host cell types including monocytes/macrophages, natural killer cells, astrocytes, megakaryocytes, and glial cell lineages [2,9-12]. HHV-6 can also be recovered in vivo from a broad range of tissues such as lymph nodes, peripheral blood mononuclear cells (PBMCs), renal tubular cells, salivary glands, and the central nervous system [13-19]. HHV-6 has also been identified in astrocytes from gliomas, suggesting a potential role in tumorigenesis [20,21].
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