Herpesvirus

1. Definition

Herpesviruses are a family of DNA viruses known as Herpesviridae, characterized by their ability to establish lifelong latent infections in the host. They can reactivate periodically, often in response to stress, immune suppression, or other triggers. There are over 100 known herpesviruses, but eight are known to infect humans.

2. Classification

• Herpes Simplex Virus Type 1 (HSV-1)
• Herpes Simplex Virus Type 2 (HSV-2)
• Varicella-Zoster Virus (VZV) (HHV-3)
• Epstein-Barr Virus (EBV) (HHV-5)
• Human Herpesvirus 6 (HHV-6)
• Human Herpesvirus 7 (HHV-7)
• Kaposi’s Sarcoma-Associated Herpesvirus (KSHV/HHV-8)

3. Structure

Herpesviruses share a common structure:

1. Core: Contains double-stranded linear DNA.
2. Capsid: Protects the viral genome.
3. Nucleocapsid: A combination of the core and capsid.
4. Tegument (Matrix): Surrounds the capsid, providing structural support and containing viral proteins essential for replication.
5. Envelope: A lipid membrane containing glycoproteins essential for host cell entry and immune evasion.

These components together form the complete virus particle, allowing efficient infection and survival in various environments.

4. Virus Replication Process (Herpesviruses)

1. Attachment and Fusion: The virus attaches to and fuses with the host cell membrane.
2. Capsid Release and Genome Expression:
   • The capsid separates, exposing the viral DNA.
   • Viral DNA is transported to the nucleus, where it is expressed.
     • Immediate-early genes (α): Initiate viral replication.
     • Early genes (β): Encode enzymes for DNA synthesis.
     • Late genes (γ): Encode structural proteins.
3. Virus Maturation: The virus acquires its envelope during assembly.
4. Release: Mature virus particles exit the cell, causing a cytopathic effect (CPE) and damaging the host cell.