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Survey of Viruses

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  1. Survey of Viruses Chapter 24

  2. Definition of a Virus Sub microscopic entity consisting of a single nucleic acid surrounded by a protein coat and capable of replication only within the living cells of bacteria, animals or plants.

  3. Definition of a Virus Obligate Intracellular Parasite

  4. Lipid Envelope Nucleic Acid Protein Capsid Virion Associated Polymerase Spike Projections Virion Structure

  5. Virion Morphology • Simple Structure • Repetitive Structure • High Level of Redundancy

  6. Helical Icosahedral Virus Morphology

  7. 1 Virus attachment and entry 1 2 Uncoating of virion 3 Migration of genome nucleic 5 acid to nucleus 4 Transcription 4 2 5 Genome replication 6 Translation of virus 3 mRNAs 7 Virion assembly 7 8 Release of new virus particles 6 8 Virus Replication

  8. Transmission of Viruses • Respiratory transmission • Influenza A virus • Faecal-oral transmission • Enterovirus • Blood-borne transmission • Hepatitis B virus • Sexual Transmission • HIV • Animal or insect vectors • Rabies virus

  9. In vivo Disease Processes • Cell destruction • Virus-induced changes to gene expression • Immunopathogenic disease

  10. Acute Virus Infections • Localised to specific site of body • Development of viraemia with widespread infection of tissues

  11. Poliovirus

  12. Poliovirus Properties of the virus • Enterovirus. • Possesses a RNA genome. • Transmitted by the faecal oral route. • Cause of gastrointestinal illness and poliomyelitis.

  13. Influenza A virus Properties of the virus • Myxovirus • Enveloped virus with a segmented RNA genome • Infects a wide range of animals other than humans • Undergoes extensive antigenic variation • Major cause of respiratory infections

  14. Influenza A virus Infection • Spread by respiratory route • Virus infects cells of the respiratory tract • Destruction of respiratory epithelium • Secondary bacterial infections • Altered cytokine expression leading to fever • e.g interleukin-1 and interferon

  15. Spread of influenza virus

  16. Respiratory Tract

  17. Other Viral Infections • Herpes • Hepatitis • Rhinovirus • HIV • Ebola • Measles • Mumps • Smallpox • Chickenpox

  18. Human H2N2 Human H3N2 Genetic Reassortment Avian H3N8 Point mutation of HA and NA genes Generation of Novel Influenza A Viruses ANTIGENIC SHIFT ANTIGENIC DRIFT

  19. Antiviral Targets • Attachment/Entry • Nucleic acid replication • Virus protein processing • Virus maturation

  20. Problems with Antivirals • Identification of virus-specific target. • Generation of resistant variants.