Transcript HERPESVIRIDAE

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
Objectives
Students 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.
Viruses grow and kill cells, this
results in cell death in vitro and
necrotic lesions in-vivo
HOSTS FOR VIRUS
CULTIVATION
1) EXPERIMENTAL ANIMALS,
4 uses
2) FERTILE HEN’S EGGS
3) CELL CULTURES
Production of cell cultures:
Continuous cell lines.
VIRUS ISOLATION
GROWTH:
The stages in virus infection are :
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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.
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.
THE EFFECTS THAT
VIRUSES HAVE ON CELLS
Cytopathic effects:
cell lysis
syncytia
transformation.
Syncytia.
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.
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.
PRESERVATION OF VIRUS
INFECTIVITY
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