Veterinary Virology

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Veterinary Virology
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Why are viruses important to vets?

• Viruses cause disease in animals of economic
  and/or welfare importance
• Diagnose viral disease (clinical/lab tests)
• Advise clients control (risk to other animals)
• Animal viruses may pose risk to human health
  (zoonosis)
• Can act as important models for human disease

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Treatment of viral disease

• Husbandry fluids, comfort
• Antibiotics to treat secondary bacterial
  infection
• Antiviral drugs (interferons/virus-specific
  inhibitors)
• Immune system modulators
• Post exposure vaccination (e.g. rabies)

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Control of viral disease

• Vaccination target or reservoir species
• Hygiene and Sanitation good management
• Isolation/Quarantine
• Eradication of reservoir/vector and possibly
  virus
• Legislation movement, exportation ( products)
• Disease Surveillance - clinical and laboratory
  diagnosis

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Virus Classification

• International Committee on Taxonomy of Viruses

chemical characteristics, genome type,
replication strategy, diseases, vectors,
geographical distribution, host
species nucleotide sequence
order family subfamily genus species/strain/type
-virales -viridae -virinae -virus -virus
mononegavirales paramyxoviridae paramyxovirinae morbillivirus canine distemper virus
herpesviridae alphaherpesvirinae varicellovirus equid herpesvirus 1
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DNA Viruses
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RNA Viruses
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Veterinary Virology (basic)

• What are viruses ?
• How do viruses replicate ?
• What effects do viruses have ?
• How do viruses change ?
• What are the consequences of change ?

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What are viruses ?
Submicroscopic particles
Nucleic acid contained within a protective
protein coat Infect bacteria, plants, animals
(inc humans)

• Differences from bacteria
• viruses CANNOT replicate outwith a cellular
  environment
• viruses ARE NOT affected by antibiotics

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Virion (virus particle) structure
1. genome
nucleocapsid
2. capsid
3. envelope
envelope glycoproteins
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1- Viral Nucleic Acids

• DNA or RNA cell genetic material is DNA
• ss or ds
• ss -//mixed sense mRNA sense
• linear or circular
• segmented/non-segmented
• size 2-300 kb(p) cell genome 3x106kbp

• Genetic heritage
• Codes for virus proteins
• Controls virus protein production
• - promoters, transcriptional enhancers,
  splice signals
• Contains elements necessary for replication and
• genome packaging

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Viral Proteins

• Structural
• Components of capsid (protective coat) and other
  components of the virion
• Non-structural
• Required for viral replication and interaction
  with host

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2- Nucleocapsid

• Capsid is protein coat that protects the nucleic
  acid
• physical, chemical, enzymatic attack
• Nucleocapsid comprises the capsid and enclosed
• nucleic acid
• facilitates entry into cell and delivery of
  nucleic acid
• exposed to immune system

genome
nucleocapsid
capsid
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• Viruses come in a variety of shapes and sizes
  dictated by their protein and nucleic acid
  composition

- but there are common elements in their
architecture due to SYMMETRY
ICOSAHEDRAL HELICAL
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Icosahedral (or cubic)
20 faces each face an equilateral triangle axes
of 2-, 3- and 5-fold rotational symmetry Capsomer
structure enclosing maximum volume
Some icosahedral animal viruses are enveloped
Foot and mouth disease virus (picornavirus)
herpesvirus
adenovirus
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Helical
Simple viruses with small genomes use this
architecture to provide protection for the genome
without the need to encode multiple capsid
proteins.
Rabies virus (rhabdovirus)
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Helical
All animal viruses with helical symmetry are
ENVELOPED
paramyxovirus
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3 Virus Envelope

• Envelopes are LIPID BILAYERS acquired from
  cellular
• membranes e.g. endoplasmic reticulum, nuclear
• membrane, plasma membrane
• viral proteins are associated with/inserted into
  
• membrane surface proteins often glycosylated

• Adsorption and entry of virus into cells (and
  exit)
• -access to target cells
• binding to receptors
• fusion of envelope with
• cellular membranes to
• release genome
• Interaction with immune system components
• - binding of antibody
• - Targets of immune system

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Complex Virus Structures
Most animal viruses fall into three structural
classes, helical capsid (enveloped) icosahedral
capsid (nonenveloped) or icosahedral capsid
(enveloped) However, more complex structures do
exist e.g. pox viruses
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Stability of Viruses

• Non enveloped viruses more hardy than enveloped
  viruses
• (e.g. foot and mouth disease hardier than
  influenza virus)
• Different viruses have differential ability to
  survive
• sensitive to temperature, pH, dessication, lipid
  solvents, detergents
• Most inactivated at gt55-60oC
• Detergents used to disrupt viral envelopes
• Rotavirus survives pH of stomach
• Clinical sample collection / Diagnostics