HHV-6

HHV-6 virus (Human herpesvirus 6) belongs to the order of Herpesvirales in the family: Herpesviridae, the subfamily: Betaherpesvirinae, the genus: Roseolovirus, the species: Human herpesvirus 6A, 6B; HHV-6A; HHV-6B. TNFRSF4 receptor protein is the receptor for this virus species.

The former viral species "Human herpesvirus 6, HHV-6 is elevated to the rank of species according to the ICTV (International Committee on Taxonomy of Viruses; 2019) into the two subtypes A and B.

Human herpesvirus type 6A and human herpesvirus type6B (HHV-6A and HHV-6B) are 2 human pathogenic species of the viral genus Roseolovirus from the Betaherpesvirus subfamily (Lautenschläger S 2018).

HHV-6A and HHV-6B are practically ubiquitously distributed viruses. At least 80 % of the adult population is seropositive.

In general, the initial infection with HHV-6B occurs in 95% of cases before the age of 2. The infection occurs by droplet infection and is usually clinically inapparent.

Symptomatic infection manifests as three-day fever(exanthema subitum).

Acute HHV-6 infection may also present with fever and status epilepticus (Mohammadpour Touserkani F et al. 2017).

In adults, primary infection is associated with a highly febrile clinical picture with maculo-papular exanthema, lymphadenopathy, possible complicating hepatitis, and meningoencephalitis (Costa BKD et al. 2019). HHV-6B-induced encephalitis is an important cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation (Ward KN et al. 2019).

HHV-6 appears to be implicated in pityriasis rosea.

HHV-6 also appears to play a pathogenetic role in the diseases listed below: Gianotti-Crosti syndrome, thrombocytopenic purpura, Stevens-Johnson syndrome, graft-versus-host reaction.

Similarly, it is suspected that there is an association between reactivation of HHV-6 and the severity of DRESS syndrome (Míguez-Martín L et al. 2019).

Furthermore, HHV-6 is thought to be a possible cofactor in basal cell carcinoma and squamous cell carcinoma. To date, no diseases have been associated with the HHV-6A species (the former HHV-6 subtype A).

The virus can be cultured from saliva or pharyngeal lavage water in lymphocyte cultures. Another possibility is the detection of its nucleic acids in blood lymphocytes by PCR.

1. Costa BKD et al (2019) Viral encephalitis: a practical review on diagnostic approach and treatment. J Pediatr (Rio J) pii: S0021-7557(19)30429-2
   Kobayashi N et al (2019) Attenuation of human herpesvirus 6B reactivation by aging. J Med Virol 91:1335-1341.
2. Lute S (2018) Human herpes viruses. In: Braun-Falco`s Dermatology, Venerology Allergology G. Plewig et al. (Hrsg) Springer Verlag S 124
3. Míguez-Martín L et al (2019) Delayed aminopenicillin reaction associated to human herpes virus 6 infection mimicking DRESS syndrome. Rev Alerg Mex 66:375-378.
4. Mohammadpour Touserkani F et al (2017) HHV-6 and seizure: A systematic review and meta-analysis. J Med Virol 89:161-169.
5. Ward KN et al (2019) Guidelines from the 2017 European Conference on Infections in Leukaemia for management of HHV-6 infection in patients with hematological malignancies and after hematopoietic stem cell transplantation. Haematologicapii: haematol.2019.223073.