HHV-7

Human herpesvirus 7 (HHV-7), like HHV-6, is a worldwide herpesvirus belonging to the family Herpesviridae, the subfamily Betaherpesvirinae and the genus Roseolovirus. The pathogen reservoir is only humans. HHV-7, like human herpesviruses 6A, 6B (HHV-6A, HHV-6B), is genetically related to cytomegalovirus. As a member of the Herpesviridae family, the complex virus has a DNA genome of about 150Kb. It is helically arranged around a core consisting of proteins and is enclosed by a capsid. The envelope contains up to 12 glycoproteins.

Transmission occurs predominantly through saliva, possibly also through droplet infection. Healthy HHV-6/7-seropositive children and adults can excrete the viruses intermittently in saliva without this having any disease value. The pathogenicity of HHV-7 is less clearly defined than that of HHV-6A and HHV-6B. Apparently, initial infection with HHV-7 occurs in childhood as an asymptomatic infection or as exanthema subitum (Ablashi DV et al. 1994). This is followed by a lifelong latency of the virus in the body. By adolescence at the latest, the infection rate is > 85 % (Ablashi DV et al. 1994). Reactivations occur in immunosuppressed patients, for example after organ transplantation. Reactivations of HHV-7, clinically associated with the appearance of pityriasis rosea, have also been demonstrated during therapy with omalizumab (Vaccaro M et al. 2020). The association of HHV-7 (HHV-6) with pityriasis rosea is likely to be largely established (Agut H et al. 2017, El-Hussein M et al. 2020, Engelmann I et al. 2018).

Further associations of HHV-7 were found in various other disease patterns, although the clinical significance of the infection is often unclear. This is also the case in fibromyalgia, where the role of the virus has not yet been clarified (Krumina A et al. 2019).

Serological diagnostics are particularly indicated for primary infections. It is considered less specific, as cross-reactivity with HHV-6 and CMV may occur. By means of gene amplification (PCR), the detection and quantification of the viral genome is possible.

Therapy of the infection with HHV-7 is usually not necessary. In immunosuppressed patients, ganciclovir, foscarnet and cidofovir are possible therapeutic agents. They inhibit the replication of (HHV-6A, HHV-6B and) HHV-7. Severe infections can be treated with them (Agut H et al. 2017).

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