Transcript Slide 1
Viruses and what they do - An overview Wednesday, August 25, 2010 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). Viral Genomes Single Stranded DNA Double Stranded Nucleic Acid RNA Double Stranded Positive Single Stranded Negative RNA DNA SS RNA genomes • +ve (sense) and -ve (anti-sense) RNA genomes Positive (sense) AUG GCA CGA Negative (anti-sense) UAC CGU GCU met ala arg herpes capsid adeno Virion “naked” virus particle or Virion envelope enveloped Virus or Virion capsomeres Capsid Proteins produced by viruses • Structural proteins • Non-structural proteins Some viral shapes papillomavirus adenovirus “naked” viruses 100 nm 1 nm = 1 millionth of a mm 100 nm = 1 ten thousandth of a mm parvovirus 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 Taxonomy • • • • What is it? On what is it based? Is it important? Do I need to remember all the details? International Committee on Taxonomy of Viruses Viruses with ss DNA genomes porcine circovirus Circoviridae canine parvovirus-2 Parvoviridae feline panleukopenia virus porcine parvovirus (SMEDI) Viruses with ds DNA genomes papillomaviruses Papovaviridae Adenoviridae Herpesviridae adenoviruses equine bovine herpesvirus-1,2 herpesviruses -1,4 porcine cytomegalovirus malignant catarrhal fever virus Poxviridae poxviruses African swine fever virus african swine fever virus Viruses with ds RNA genomes rotaviruses Reoviridae bluetongue virus african horse sickness Birnaviridae infectious bursal disease (chickens) infectious pancreatic necrosis (salmonid fish) Viruses with +ve RNA genomes Picornaviridae Caliciviridae Coronaviridae Arteriviridae Flaviviridae Togaviridae foot and mouth disease virus porcine enteroviruses feline calicivirus coronaviruses equine arterivirus, PRRS flaviviruses (WNV) pestiviruses (BVD) equine encephalitis viruses Viruses with -ve RNA genomes Orthomyxoviridae Paramyxoviridae influenzaviruses parainfluenza virus canine distemper virus Hendra, Nipah viruses respiratory syncytial virus Rhabdoviridae rabies virus Filoviridae vesicular stomatitis virus Ebola virus Bunyaviridae Haantan virus Viruses with reverse transcriptase feline leukemia virus Retroviridae feline, bovine immunodeficiency viruses bovine, avian leukosis viruses caprine arthritis-encephalitis virus Hepadnaviridae Antigenic classification: Serotypes and Groups How new serotypes arise – gradual changes in external proteins due to pressure by neutralizing antibodies no selective pressure on internal proteins selective pressure on external viral proteins antibodies to all viral proteins antibodies to external proteins neutralize virus 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 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 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 process repeated, over time same serotype neutralizes neutralizes neutralizes new serotype neutralizes does not neutralize serum from original cat NOTE: Only external proteins change. Internal proteins do not change 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 process repeated, over time same serotype new serotype different serotypes same group 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 Group and type specific antigens type specific antigen “naked” virus (eg FMDV) group specific antigen enveloped virus (eg influenza, FeLV) 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 type specific antigen example - influenza serotype H1 group specific antigen serotype H5 test based on group specific antigen will detect all three serotype H7 vaccination against one serotype will not protect against others Infection of a cell Stage Biological Host Drug implications defenses intervention Distribution of the CCR532 mutation in human populations from PLoS Biology, Nov 2005 Errors in replication lead to “quasispecies” persistent infection mixture of variant viruses (quasispecies) inclusion bodies Release of virus Release by lysis of cell (cytopathic) or by budding (without death of cell, non-cytopathic)