Human Herpes Virus 6 (HHV-6)

Human herpesvirus 6 was the sixth herpesvirus discovered.

Isolated in 1986 during attempts to find novel viruses in patients with lymphoproliferative diseases

HHV-6 is now recognized as a T-lymohotrophic virus with high affinity for CD4 lymphocytes.

HHV-6 has two variants, A and B.

1. HHV-6B causes the childhood illness roseola infantum, characterized by abrupt high fever and mild sore throat and rash.
2. HHV-6A has been isolated mainly in immunocompromised hosts, characterized by manifestation as a mononucleosislike illness with fever, lymphadenopathy, and hepatitis or encephalitis, with negative test results for CMV or Epstein-Barr virus (EBV).

HHV-6 has been isolated from various tissues, cells, and fluid in association with the following conditions:

• Kikuchi lymphadenitis
• Lymphoma
• Lymphadenopathy
• Drug-induced hypersensitivity syndrome³
• Sarcoidosis
• Systemic lupus erythematosus
• Chronic fatigue syndrome
• Guillain-Barré syndrome
• MS

A causal relationship has not been yet been established between HHV-6 and these conditions.

 

In vivo, HHV-6 primarily infects and replicates in CD4 lymphocytes. The cellular receptor is CD46, a 52- to 57-kDa type 1 transmembrane glycoprotein expressed on the surface of all cells. The cell attachment protein of HHV-6 has not been identified. Entry occurs through receptor-mediated endocytosis. Subsequent stages of viral replication are similar to those of CMV.

Pathology:

• HHV-6 infection is the most common cause of febrile seizures in childhood (age 6-24 mo).
• Encephalitis may develop in children with HHV-6 infection.
• HHV-6 has a possible role in CNS infections and demyelinating conditions.
• HHV-6 infection may increase the severity of CMV infection in immunocompromised and transplant populations.
• HHV-6 has a possible role in lymphoproliferative syndromes.
• HHV-6 infection induces bone marrow suppression, respiratory failure, graft versus host disease, and encephalitis in patients undergoing hematopoietic stem cell or solid-organ transplantation.

Miele, Peter, S, Salvaggio, Michelle,  R and Smith, Margo, A. 2010. Humanherpes Virus Type 6. Retrieved February, 2, 2010 from http://emedicine.medscape.com/article/219019-overview.