Definition of Herpesvirus

Herpesvirus: One of a family of double-stranded DNA viruses that cause common infections in humans. These include: herpes, CMV, chickenpox, shingles, mono, measles, and Kaposi sarcoma.

The herpesviruses may live latently in a person for years or even decades without causing symptoms and then be activated and cause disease. The human herpesviruses are:

• Human herpesvirus 1 (HHV-1) -- The herpes simplex virus type 1 (HSV-1) which causes oral herpes.

• Human herpesvirus 2 (HHV-2) -- The herpes simplex virus type 2 (HSV-2) which causes genital herpes.

• Human herpesvirus 3 (HHV-3) -- The cytomegalovirus (CMV).

• Human herpesvirus 4 (HHV-4) -- The varicella-zoster virus (VZV) which causes chickenpox and shingles.

• Human herpesvirus 5 (HHV-5) -- The Epstein-Barr virus (EBV) which causes infectious mononucleosis.

• Human herpesvirus 6 (HHV-6) -- There are two types. Type A is rare, and acquired in adulthood. B is relatively common, usually acquired in childhood, and associated with roseola (measles).

• Human herpesvirus 7: (HHV-7) -- Closely related to HHV-6. Also been associated with roseola (measles).

• Human herpesvirus 8: (HHV-8) -- The virus that causes Kaposi sarcoma.

The formal name of the herpesvirus family is herpesviridae. All members of this family are double-stranded DNA viruses with large complex genomes that replicate in the nucleus of the cell. Their genomes contain 60 to 120 genes. Because replication occurs inside the host nucleus, herpesviruses can use the host's transcription machinery and DNA repair enzymes to support a large genome with complex arrays of both essential or so-called dispensable genes. The essential genes regulate transcription and are needed to construct the virion. The dispensable genes enhance the cellular environment for virus production, defend the virus from the host immune system and promote cell to cell spread. The large numbers of dispensable genes are in reality required for a productive in vivo infection. It is only in the laboratory environment of cell culture that they are dispensable.