Viral Infection

Structure of viruses

  • Contain either DNA or RNA
  • Capsid made up of repeated subunits of a virally encoded protein
  • Icosahedral symmetry: virus consists of repeated subunits that make up equilateral triangles arranged in a symmetrical fashion
  • Helical symmetry: made up of a single repeated unit

Viruses and disease

  1. Viral replication
  1. Attachment - interact with specific receptors in target cell
  1. Entry - endocytosis
  1. Uncoating - viral nucleic acid released from capsid
  1. Nucleic acid and protein synthesis – host ribosomes used (host polymerases may also be used) to produce new viral proteins
  1. Assembly - nucleic acids and proteins packaged together
  1. Release
      • Budding - virus released with envelope derived from host cell membrane, doesn’t kill cell
      • Lysis - viruses accumulates until cell bursts, killing cell

Pathogenesis

  • Cell death due to lysis
  • Cell death due to immune system
  • Cell proliferation - cancer

Immune response

  • Cytotoxic T lymphocytes - recognise foreign cell surface proteins, signal to infected cell to commit suicide
  • Neutralising antibodies - IgG, IgM

Viral persistence

  • Virus may become quiescent - no active replication
    • May reactivate after a period of latency
  • Viruses may remain continually active for years - chronic infection