Human Herpesvirus 6
المؤلف:
Stefan Riedel, Jeffery A. Hobden, Steve Miller, Stephen A. Morse, Timothy A. Mietzner, Barbara Detrick, Thomas G. Mitchell, Judy A. Sakanari, Peter Hotez, Rojelio Mejia
المصدر:
Jawetz, Melnick, & Adelberg’s Medical Microbiology
الجزء والصفحة:
28e , p493
2025-11-16
46
The T-lymphotropic HHV-6 was first recognized in 1986. Initial isolations were made from cultures of peripheral blood mononuclear cells from patients with lymphoproliferative disorders.
Properties of the Virus
The viral DNA is about 160–170 kbp in size and has a mean composition of 43–44% (G + C). The genetic arrangement of the HHV-6 genome resembles that of human CMV.
HHV-6 appears to be unrelated antigenically to the other known human herpesviruses except for some limited cross reactivity with HHV-7. Isolates of HHV-6 segregate into two closely related but distinct antigenic groups (designated A and B).
The virus grows well in CD4 T lymphocytes. Other cell types also support viral replication, including B cells and cells of glial, fibroblastoid, and megakaryocyte origin. Cells in the oropharynx must become infected because virus is present in saliva. It is not known which cells in the body become latently infected. Human CD46 is the cellular receptor for the virus.
Epidemiology and Clinical Findings
Seroepidemiologic studies using immunofluorescence tests for serum antibodies or PCR assays for viral DNA in saliva or blood cells have shown that HHV-6 is widespread in the population. It is estimated that more than 90% of children older than age 1 year and adults are virus positive.
Infections with HHV-6 typically occur in early child hood. This primary infection causes exanthem subitum (roseola infantum, or “sixth disease”), the mild common childhood disease characterized by a high fever and skin rash. The 6B variant appears to be the major cause of this disease. The virus is associated with febrile seizures in children.
The mode of transmission of HHV-6 is presumed to be via oral secretions. The fact that it is a ubiquitous agent suggests that it must be shed into the environment from an infected carrier.
Infections persist for life. Reactivation appears to be common in transplant patients and during pregnancy. The consequences of reactivated infection remain to be determined. HHV-6 reactivation occurs in close to half of patients who undergo hematopoietic stem cell transplantation and can be detected using blood PCR. Those reactivations commonly occur soon after transplant and have been associated with delayed engraftment, central nervous system dysfunction, and increased mortality.
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