Viruses and what they do -

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. How new serotypes arise – gradual changes in external proteins due to pressure by neutralizing antibodies Antigenic classification: Serotypes and Groups

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

19. selective pressure on external viral proteins antibodies to all viral proteins antibodies to external proteins neutralize virus selective pressure forces selection of virions with slightly different external proteins

20. 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

21. 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

22. 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

23. 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

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

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

27. 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

28. 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

29. Infection of a cell

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

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

32. inclusion bodies

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