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Veterinary Virology

Veterinary Virology. 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)

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Veterinary Virology

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  1. Veterinary Virology

  2. 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

  3. Treatment of viral disease • Husbandry – fluids, comfort • Antibiotics – to treat secondary bacterialinfection • Antiviral drugs (interferons/virus-specific inhibitors) • Immune system modulators • Post exposure vaccination (e.g. rabies)

  4. 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

  5. Virus Classification International Committee on Taxonomy of Viruses chemical characteristics, genome type, replication strategy, diseases, vectors, geographical distribution, host species nucleotide sequence

  6. DNA Viruses

  7. RNA Viruses

  8. 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 ?

  9. 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

  10. Virion (virus particle) structure 1. genome nucleocapsid 2. capsid ± 3. envelope envelope glycoproteins

  11. 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

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

  13. 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

  14. 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

  15. 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

  16. 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)

  17. Helical All animal viruses with helical symmetry are ENVELOPED paramyxovirus

  18. 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

  19. 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

  20. 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 >55-60oC • Detergents used to disrupt viral envelopes • Rotavirus survives pH of stomach • Clinical sample collection / Diagnostics

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