VIRUS PICTURES: Herpesviruses: image of Herpes Virus Replication or Life Cycle

EXPLANATION OF HERPES VIRUS REPLICATION IMAGE

At upper right a virus particle lands on a cell and docks with cell surface proteins. The viral envelope then fuses with the plasma membrane of the cell and the viral capsid (blue) containg the viral genome (red) and tegument proteins enter the cytoplasm. The capsid then travels along a microtubule towards the nucleus where it docks with a nuclear pore (flower like structure embedded in the purple nuclear envelope). The viral DNA enters the nucleus through the pore and circularises before replication. New viral capsids assemble in the nucleus and daughter genomes are taken into them (bottom right). The capsids bud through the inner nuclear envelope gaining a temporary envelope that surrounds them during their (short) stay in the perinuclear space. This envelope then fuses with the outer nuclear envelope and the now naked capsids progress through the cytoplasm until they bud into Golgi vesicles laden with viral proteins. This budding into the vesicle furnishes the developing virion with tegument proteins, an envelope and surface projections. The vesicle delivers the contained virion to the cell surface. The vesicle fuses with the plasma membrane and the new virus particle is free to infect another cell.

HERPES VIRUSES: The Herpesviruses (family herpesviridae) are a very important group of double stranded DNA viruses that replicate inside the nuclei of their host cells. They have many characteristics in common including:

• double stranded DNA genome (dsDNA)
• icosahedral capsid
• tegument
• envelope with "glycoprotein spikes"

The herpesviruses cause many major diseases. Below is a list of the viruses with some of their associated diseases:

HERPESVIRUSES family Herpesviridae

Alphaherpesviruses subfamily Alphaherpesvirinae (neurotropic)

• Herpes simplex virus (HSV-1 + HSV-2):
  • oral herpes (cold sores)
  • genital herpes
  • congenital herpes (neonatal herpes) can cause blindness and neurological problems
  • keratoconjunctivitis (ocular herpes)
  • herpes encephailitis
  • herpes meningitis
• Varicella-Zoster Virus (VZV):
  • chickenpox
  • shingles (herpes zoster)

Betaherpesviruses subfamily Betaherpesvirinae

• Cytomegaloviruses (CMV) or Human herpesvirus 5 (HHV-5)
• Human Herpes Virus 6 (HHV-6):
  • exanthem subitum / sixth disease / roseola infantum
• Human Herpes Virus 7 (HHV-7)

Gammaherpesviruses subfamily Gammaherpesvirinae (lymphotropic)

• Epstein-Barr Virus (EBV):
  • Hodgkin's Disease
  • Burkitt's lymphoma
  • infectious mononucleosis (mono) or kissing disease
• Human Herpes Virus 8 (HHV-8) or Kaposi's Sarcoma-Associated Herpesvirus (KSHV):
  • Kaposi's sarcoma