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Viruses and what they do -

Viruses and what they do -. An overview. Wednesday, August 25, 2010. Viruses (Encyclopedia Britannica).

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Viruses and what they do -

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  1. Viruses and what they do - An overview Wednesday, August 25, 2010

  2. Viruses (Encyclopedia Britannica) ..infectious agents of small size and simple composition that can multiply only in living cells of animals, plants and bacteria. Viruses are obligate parasites that are metabolically inert when they are outside their hosts. They all rely, to varying extents, on the metabolic processes of their hosts to reproduce themselves. The viral diseases we see are due to the effects of this interaction between the virus and its host cell(and/or the host’s response to this interaction).

  3. Viral Genomes Single Stranded DNA Double Stranded Double Stranded Nucleic Acid Positive Single Stranded RNA Negative RNA DNA

  4. +ve (sense) and -ve (anti-sense) RNA genomes Positive (sense) Negative (anti-sense) SS RNA genomes AUG GCA CGA met ala arg UAC CGU GCU

  5. adeno Virion capsid herpes “naked” virus particle or Virion envelope capsomeres enveloped Virus or Virion Capsid

  6. Structural proteins Non-structural proteins Proteins produced by viruses

  7. Some viral shapes papillomavirus adenovirus “naked” viruses 100 nm parvovirus 1 nm = 1 millionth of a mm 100 nm = 1 ten thousandth of a mm

  8. Some viral shapes 1 nm = 1 millionth of a mm 100 nm = 1 ten thousandth of a mm 100 nm influenzavirus parainfluenza virus Enveloped viruses herpesvirus poxvirus

  9. What is it? On what is it based? Is it important? Do I need to remember all the details? Taxonomy International Committee on Taxonomy of Viruses

  10. Viruses with ss DNA genomes porcine circovirus Circoviridae canine parvovirus-2 Parvoviridae feline panleukopenia virus porcine parvovirus (SMEDI)

  11. Viruses with ds DNA genomes papillomaviruses Papovaviridae adenoviruses Adenoviridae equine herpesviruses -1,4 bovine herpesvirus-1,2 Herpesviridae porcine cytomegalovirus malignant catarrhal fever virus Poxviridae poxviruses African swine fever virus african swine fever virus

  12. Viruses with ds RNA genomes rotaviruses Reoviridae bluetongue virus african horse sickness Birnaviridae infectious bursal disease (chickens) infectious pancreatic necrosis (salmonid fish)

  13. Viruses with +ve RNA genomes foot and mouth disease virus Picornaviridae porcine enteroviruses Caliciviridae feline calicivirus Coronaviridae coronaviruses Arteriviridae equine arterivirus, PRRS Flaviviridae flaviviruses (WNV) pestiviruses (BVD) Togaviridae equine encephalitis viruses

  14. Viruses with -ve RNA genomes influenzaviruses Orthomyxoviridae parainfluenza virus canine distemper virus Paramyxoviridae Hendra, Nipah viruses respiratory syncytial virus Rhabdoviridae rabies virus vesicular stomatitis virus Filoviridae Ebola virus Bunyaviridae Haantan virus

  15. Viruses with reverse transcriptase feline leukemia virus Retroviridae feline, bovine immunodeficiency viruses bovine, avian leukosis viruses caprine arthritis-encephalitis virus Hepadnaviridae

  16. Isolates, strains, serotypes and groups

  17. no selective pressure on internal proteins selective pressure on external viral proteins antibodies to all viral proteins antibodies to external proteins neutralize virus

  18. selective pressure on external viral proteins antibodies to all viral proteins antibodies to external proteins neutralize virus selective pressure forces slight change in external proteins

  19. virus, including changed virus, passed on to new host selective pressure on external viral proteins antibodies to all viral proteins antibodies to external proteins neutralize virus selective pressure forces slight change in external proteins

  20. process repeated, over time….. neutralizes neutralizes neutralizes neutralizes does not neutralize serum from original cat NOTE: Only external proteins change. Internal proteins do not change

  21. process repeated, over time same serotype new serotype neutralizes neutralizes neutralizes neutralizes does not neutralize serum from original cat NOTE: Only external proteins change. Internal proteins do not change

  22. Serotype - all isolates of a virus that can be neutralized by a common antiserum are said to belong to the same serotype. …..because of changes in external protein (internal proteins do not change) external proteins are called TYPE SPECIFIC antigens internal proteins are called GROUP SPECIFIC antigens

  23. process repeated, over time same serotype new serotype different serotypes same group

  24. Group and type specific antigens type specific antigen “naked” virus (eg FMDV) enveloped virus (eg influenza, FeLV) group specific antigen

  25. Groups, types (sero-types), isolates and ‘strains’ Type -A specific antigen Type -A Type - B Group specific antigen isolate Type - C Group Type - C specific antigen

  26. Serotypes and neutralizing antibody (eg. FMDV) A C O SAT1 SAT2 SAT3 Asia serotypes of FMD virus receptor receptor binding protein on viral surface antibodies against receptor binding protein of serotype A will neutralize viruses of serotype A but not of serotype C

  27. example - influenza type specific antigen serotype H1 serotype H5 serotype H7 group specific antigen test based on group specific antigen will detect all three vaccination against one serotype will not protect against others

  28. Infection of a cell • attachment • entry and uncoating • viral gene expression • genome replication • DNA viruses • RNA viruses • assembly and release • naked viruses • enveloped viruses

  29. Distribution of the CCR532 mutation in human populations from PLoS Biology, Nov 2005

  30. Errors in replication lead to “quasispecies” persistent infection mixture of variant viruses (quasispecies)

  31. inclusion bodies A B C D

  32. Release of virus or by budding (without death of cell, non-cytopathic) Release by lysis of cell (cytopathic)

  33. Infection of a cell

  34. Infection of the animal Entry - the beginning of infection Local replication vs systemic spread Consequences of infection none to illness (signs, symptoms) Signs and symptoms Why some animals get sick while others do not Patterns of disease

  35. Why do some infected animals get sick and others don’t? Viral factors - virulence Host Factors

  36. Viral Factors:Why are some isolates of a virus more likely to cause severe disease than others?determinants of viral virulence

  37. Host Factors: Genetic Resistance loss of receptors CCR5-D32 mutation and resistance to HIV variation in immune response genes genetic defects in defenses

  38. Host factors: age related susceptibility greater susceptibility of new born animals greater susceptibility of adults prior exposure, acquired resistance maternal protection concurrent infections, immuno-suppression, increase in susceptible cells

  39. Incubation period infection incubation period - time between infection and the appearance of clinical signs

  40. Patterns of disease clinical signs virus shedding acute virus difficult to detect recurrent chronic or persistent slow

  41. Resistance and Recovery

  42. Resistance and recovery innate resistance genetic serum, mucous factors (complement, defensins) induced resistance Toll-like receptors (dendritic cells) Pathogen Associated Molecular Patterns interferons and inflammatory cytokines acquired immunity humoral cell mediated

  43. After the Toll Rush, LAJ O’Neill, Science 303:1481 2004

  44. Interferons I I I I I activated E factor antiviral effects infected Immune Modulation cell Induced interferon genes

  45. Acquired anti-viral immunity (antibody) Virus neutralized B Virus infected cell Antibody targets Fc receptor bearing cell To kill virus infected cell

  46. Acquired immunity (CMI) perforins necrosis CD8 Apoptosis trigger apoptosis CD4 cytokines virus replication suppressed

  47. Prevention of infection and/or disease

  48. Protection of the new born animal antibodies (possible CMI as well) in colostrum maternal immunization colostrum replacers implications for immunization of young animals caution when using modified-live vaccines interference by maternal antibodies

  49. Interference by maternal antibodies * window of susceptibility minimum amount needed for protection * interferes with vaccination * passive antibody * * * can vaccinate in this range 2 4 6 8 10 12 weeks after birth

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