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Chapter 23 : Human Herpesvirus 6 and Human Herpesvirus 7
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Human herpesvirus 6 (HHV-6) was first isolated from patients with lymphoproliferative disorders in 1986 and was initially named human B-lymphotropic virus. Characterization of HHV-6 indicated that the virus is antigenically and genetically distinct from other known human herpesviruses. HHV-7 can be frequently isolated from saliva of healthy adults, and horizontal transmission of HHV-7 may occur even from grandparents or parents to children through close household contact. Thus, the modes of transmission of HHV-6 and -7 are very similar; however, it is not clear why HHV-7 infection occurs generally later than HHV-6 infection. Western blotting and immunofluorescent-antibody assay (IFA) demonstrated the presence of HHV-6 antibody in monkeys. HHV-6 DNA can be detected by DNA hybridization and by PCR. Variant-specific oligonucleotide hybridization is based on the amplification of two distinct regions of the HHV-6 genome, followed by hybridization of amplimers with variant-specific oligonucleotide probes. The primer sequences, based on consensus sequences in the DNA polymerase gene of herpesviruses, can be used for testing six different herpesviruses simultaneously. Comparison of the multiplex assay with the respective single PCR assays using cloned HHV-6 and HHV-7 sequences as targets for amplification demonstrated equivalent sensitivities and specificities of the assays. This multiplex assay is an efficient and cost-effective approach to the analysis of large numbers of samples to determine the epidemiological importance of HHV-6 and -7. Several serologic assays are available for HHV-6 studies, including IFA, enzyme-linked immunosorbent assay, neutralization, radioimmunoprecipitation, and immunoblotting.
Key Concept Ranking
- Major Histocompatibility Complex Class I
Herpesvirus particles seen outside of HHV-6-infected cells.
Predicted ORF organization of HHV-6 strain HST. Repeat regions (DRL, DRR, R1, R2, and R3) are boxed, telomeric repeat regions (T1 and T2) are indicated above the DRs, and UR is indicated by a solid line. Protein coding regions are indicated as open arrows and are numbered DR1, DR2, DR3, DR6, DR7, DR8, DRHN1, and DRHN2 within the direct repeats and HN1, HN2, HN3, and U1 to U100 (excluding U78, U88, U92, U93, and U96) within the UR. The origin of replication (Ori) is indicated by an asterisk. The US22 gene family is shaded. Abbreviations not used in the text: GCR, G-protein-coupled receptor; Ig, Ig immunoglobulin superfamily; RR, large subunit of ribonucleotide reductase; mCP, minor capsid protein; CA, capsid assembly protein; Teg, tegument protein; Pol, DNA polymerase; tp, transport protein; mDBP, major single-stranded DNA binding protein; TA, conserved herpesvirus transactivator; dUT, dUTPase; Pts, protease/assembly protein; pp65/71, phosphoprotein 65/71K; MCP, major capsid protein; PT, phosphotransferase; Exo, exonuclease; OBP, origin binding protein; Hel, helicase; UDG, uracil-DNA glycosylase; Che, chemokine; AAV rep1, adeno-associated virus replication protein homolog. (Reprinted from reference 56 with permission.)
CPE by HHV-6. Note the balloon-like cells around clumps of lymphocytes.
Clinical feature (typical rash) of a patient with ES.