Herpesviruses

Name comes from the Greek 'Herpein' - 'to creep' = chronic/latent/recurrent infections. Epidemiology of the common Herpesvirus infections puzzled clinicians for many years. In 1950, Burnet and Buddingh showed that HSV could become latent after a primary infection, becoming reactivated after later provocation. Weller (1954) isolated VZV from chicken pox and zoster, indicating the same causal agent. ~100 Herpesviruses have been isolated, at least one for most animal species which has been looked at. To date, there are 8 known human Herpesviruses.
The family is divided into 3 sub-families:

Alphaherpesvirinae:
Simplexvirus	human herpesvirus 1, 2 (HSV-1, HSV-2)
Varicellovirus	human herpesvirus 3 (VZV)

Betaherpesvirinae:
Cytomegalovirus	human herpesvirus 5 (HCMV)
Muromegalovirus	mouse cytomegalovirus 1
Roseolovirus	human herpesvirus 6, 7 (HHV-6, HHV-7)

Gammaherpesvirinae:
Lymphocryptovirus	human herpesvirus 4 (EBV)
Rhadinovirus	human herpesvirus 8 (HHV-8)

Large (genomes up to 235kbp DNA) and complex viruses ~35 virion proteins. All encode a variety of enzymes involved in nucleic acid metabolism, DNA synthesis and protein processing (protein kinase). The Herpesviruses are widely separated in terms of genomic sequence and proteins, but all are similar in terms of virion structure and genome organization:

Size: 180-200nm

Envelope: Present; associated glycoproteins.

Tegument: Protein-filled region between capsid and envelope.

Capsid: Icosahedral, 95-105nm diameter; 162 hexagonal capsomers.

Core: Toroidal (DNA around protein), ~75nm diameter.

Genome: Linear, d/s DNA, 105-235kbp

Replication: Nuclear.

Assembly: Nuclear.

Common Antigens: None!

Size:	180-200nm
Envelope:	Present; associated glycoproteins.
Tegument:	Protein-filled region between capsid and envelope.
Capsid:	Icosahedral, 95-105nm diameter; 162 hexagonal capsomers.
Core:	Toroidal (DNA around protein), ~75nm diameter.
Genome:	Linear, d/s DNA, 105-235kbp
Replication:	Nuclear.
Assembly:	Nuclear.
Common Antigens:	None!

Structure:

The structure of the herpesvirus particle is very complex. The core consists of a toroidal shape with the large DNA genome would around a proteinaceous core. The complex capsid surrounds the core. Outside the capsid is the tegument, a protein-filled region which appears amorphous in electron micrographs. On the outside of the particle is the envelope, which contains numerous glycoproteins (see discussion of Herpes Simplex Virus, below). To view an electron micrograph of negatively-stained herpesvirus particles click here. N.B. All herpesviruses are almost indistinguishable in electron micrographs.

To view an image of the herpesvirus capsid click here.

Genome:

All herpesvirus genomes have a unique long (UL) and a unique short (US) region, bounded by inverted repeats. The repeats allow rearrangements of the unique regions and Herpesvirus genomes exist as a mixture of 4 isomers. Herpesvirus genomes also contain multiple repeated sequences and depending on the number of these, genome size of various isolates of a particular virus can vary by up to 10kbp.

Herpesviruses

Structure:

Genome:

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