VIRUS REPLICATION

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VIRUS REPLICATION

• PETER H. RUSSELL, BVSc, PhD, FRCPath, MRCVS
• Department of Pathology and Infectious Diseases,
  The Royal Veterinary College,
• Royal College Street,
• London NW1 OTU.
• E-mail Web site

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ObjectivesStudents should be able to

• describe in outline how to cultivate viruses
• list the stages of virus replication in a host
  cell with reference to how these differ between
  RNA and DNA viruses.
• explain the effects that viruses have on cells.

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Viruses grow and kill cells, this results in cell
death in vitro and necrotic lesions in-vivo
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HOSTS FOR VIRUS CULTIVATION

• 1) EXPERIMENTAL ANIMALS, 4 uses

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2) FERTILE HENS EGGS
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3) CELL CULTURES
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Production of cell cultures
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Continuous cell lines.
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VIRUS ISOLATION
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GROWTH
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The stages in virus infection are

• 1) Attachment
• 2) Penetration and uncoating
• 3) Formation of viral messenger RNA
• 4) Formation of new genomes
• 5) Formation of new protein
• 6) Assembly.
• 7) Release
• 8) Latency.

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The stages in virus infection are

• 1) Attachment
• 2) Penetration and uncoating
• 3) Formation of viral messenger RNA
• 4) Formation of new genomes
• 5) Formation of new protein
• 6) Assembly.
• 7) Release
• 8) Latency.

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THE EFFECTS THAT VIRUSES HAVE ON CELLS
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Cytopathic effectscell lysissyncytiatransforma
tion.
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Syncytia.
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Transformation

• The cells stop being flat but round up and start
  dividing uncontrollably to become piles of round
  cells eg after infection by feline sarcoma virus.
  
• Similar cells can also be cultured from some
• virus-induced tumours e.g. Feline leukaemia
  virus, Mareks disease of chickens. The virus does
  not kill the cells.

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VIRUS INFECTIVITY

• Infectivity is relevant to diagnosis to find out
  which tissues contain most virus and therefore
  are best for sampling. 100 infectious units of
  virus are often used to tests for neutralising
  antibody in a serum sample.

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PRESERVATION OF VIRUS INFECTIVITY
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Summary

• Viruses grow in susceptible hosts eg cells, eggs
  or animals
• Viruses utilise the host cells and its enzymes to
  make several hundred particles overnight.
• Certain viruses have their own enzymes because
  they undergo steps which the host cell does not,
  eg RNA to RNA
• All viruses must attach to host cell receptors.
  This often determines their host range.
• After entry viruses uncoat to release their
  nucleic acid and are not infectious at this
  stage.
• The internal virus proteins are assembled in
  discrete areas which appear as inclusion bodies.
  These are usually in the nucleus for DNA viruses
  and in the cytoplasm for RNA viruses.
• Viruses leave the cell when it dies although some
  enveloped viruses bud-off living cells