Virus morphology & classification

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Virus morphology & classification

  1. 1. VIRUS MORPHOLOGY & CLASSIFICATION ELIZABETH P. QUILES, M.D., FPASMAP OUR LADY OF FATIMA UNIVERSITY COLLEGE OF MEDICINE
  2. 2. <ul><li>Not cells </li></ul><ul><li>Smallest infectious agent (20nm to 300 nm) </li></ul><ul><ul><li>smallest RNA virus  Picornavirus </li></ul></ul><ul><ul><li>smallest DNA virus  Parvovirus </li></ul></ul><ul><ul><li>largest virus  Poxvirus </li></ul></ul>
  3. 3. <ul><li>Most have spherical shapes EXCEPT </li></ul><ul><ul><li>Rhabdovirus  bullet-shaped </li></ul></ul><ul><ul><li>Poxvirus  brick-shaped </li></ul></ul><ul><ul><li>Bacteriophage  tadpole-shaped </li></ul></ul><ul><ul><li>Tobacco Mosaic virus  rod-shaped </li></ul></ul>
  4. 4. <ul><li>Composed of only one type of nucleic acid </li></ul><ul><li>Obligate intracellular parasites  inert in the extracellular environment  multiply only in living cells  parasites at the genetic levels </li></ul>
  5. 5. <ul><li>Do not undergo mitosis or binary fission </li></ul><ul><li>Do not have cell wall & ribosome </li></ul><ul><li>Sensitive to interferon </li></ul>
  6. 6. STRUCTURE <ul><li>VIRAL NUCLEIC ACID (GENOME) </li></ul><ul><ul><li>contain the genetic material necessary for replication </li></ul></ul><ul><ul><li>either a DNA or RNA </li></ul></ul><ul><ul><li>maybe single-stranded or double-stranded </li></ul></ul>
  7. 7. <ul><ul><li>can be linear or circular </li></ul></ul><ul><ul><li>Segmented or nonsegmented </li></ul></ul><ul><ul><li>haploid  contain only one copy of their genes EXCEPT Retroviruses </li></ul></ul><ul><ul><li>used as major criterion in the classification of viruses </li></ul></ul>
  8. 8. <ul><li>CAPSID </li></ul><ul><ul><li>protein coat made up of repeating subunits  CAPSOMERES (gives the virus its geometric symmetry) </li></ul></ul><ul><ul><li>2 forms of symmetry: </li></ul></ul><ul><ul><li>1. icosahedral – capsomeres arranged in 20 triangles </li></ul></ul><ul><ul><li>2. helical – arranged in a hollow coil that appears rod-shaped </li></ul></ul>
  9. 9. HELICAL SYMMETRY
  10. 10. ICOSAHEDRAL SYMMETRY
  11. 11. <ul><ul><li>Functions of the viral capsid: </li></ul></ul><ul><ul><li>1. protect the genetic material </li></ul></ul><ul><ul><li>2. site of receptors  mediate attachment </li></ul></ul><ul><ul><li>3. serve as antigenic determinants </li></ul></ul><ul><ul><li>4. induce antibody production </li></ul></ul><ul><ul><li>5. determinants of type specificity </li></ul></ul><ul><ul><li>6. Provide the structural symmetry of the virus </li></ul></ul>
  12. 12. <ul><li>ENVELOPE </li></ul><ul><ul><li>a lipoprotein derived from the host cell membrane & virus specific protein </li></ul></ul><ul><ul><li>composed of glycoproteins (peplomers) that appear as spikes </li></ul></ul><ul><ul><li>Acquired through budding from the host’s cell membrane in the course of maturation </li></ul></ul>
  13. 13. <ul><ul><li>Confers instability to the virus because of the loss of infectivity due to disruption or loss of lipid  more sensitive to heat, detergents & lipid solvents </li></ul></ul>
  14. 14. <ul><ul><li>Functions: </li></ul></ul><ul><ul><li>1. site of receptors  attach to host cell receptors & membrane fusion </li></ul></ul><ul><ul><li>2. antigenic determinants </li></ul></ul><ul><ul><li>3. stimulate antibody production </li></ul></ul><ul><ul><li>4. determinants of type specificity </li></ul></ul>
  15. 15. TERMINOLOGIES <ul><li>VIRION – a complete viral particle </li></ul><ul><li>- in naked viruses  virion is identical to the nucleocapsid </li></ul><ul><li>- in enveloped viruses  must acquire envelop before it is considered a virion </li></ul><ul><li>NUCLEOPCAPSID – a protein-nucleic acid complex </li></ul>
  16. 16. ATYPICAL VIRUS-LIKE AGENTS <ul><li>DEFECTIVE VIRUSES – composed of nucleic acid & proteins but cannot replicate without a helper virus </li></ul><ul><li>PSEUDOVIRION – contain host cell DNA instead of viral DNA within the capsid </li></ul>
  17. 17. <ul><li>VIROIDS – consist solely of a single molecule of circular RNA without a protein coat or envelope </li></ul><ul><li>PRIONS – infectious protein particles composed solely of proteins </li></ul>
  18. 18. Yes No Inflammatory Response Yes No Antibody Response Icosahedral or helical Amyloid-like Appearance Yes No Heat Inactivation Yes, encoded by viral genes Yes, encoded by cellular genes Protein Yes No Nucleic acid CONVENTIONAL VIRUSES PRIONS FEATURE
  19. 19. VIRUS CLASSIFICATION <ul><li>Virion morphology - size, shape, symmetry, +/- of peplomers, +/- of membrane </li></ul><ul><li>Virus genome – DNA or RNA, size, strandedness, segments </li></ul><ul><li>Physicochemical properties of the virion – molecular mass, bouyant density, stability & susceptability </li></ul>
  20. 20. <ul><li>Antigenic properties </li></ul><ul><li>Virus protein properties – number, size, activities </li></ul><ul><li>Biological properties – host range, MOT, vector relationships, pathogenicity, tissue tropism & pathology </li></ul>
  21. 21. Vaccinia, Variola, Molluscum contangiosum DS, linear Complex + Poxviruses HSV, VZV, CMV, EBV, HHV6 DS, linear Icosahedral + Herpesviruses Hepatitis B virus DS, incomplete circular Icosahedral + Hepadnavirus Adenoviruses DS, linear Icosahedral - Adenovirus HPV, Polyoma DS, circular Icosahedral - Papovavirus B19 virus SS, linear Icosahedral - Parvovirus IMPORTANT VIRUSES DNA STRUCTURE SYMMETRY ENVELOPE FAMILY
  22. 22. Orthoviridae, Bunyaviridae Rhabdoviridae, Paramyxoviridae, Filoviridae SS segmented SS Enveloped Helical Flaviviridae Arenaviridae Coronaviridae Retroviridae SS SS segmented SS SS diploid Enveloped Unknown or complex Togaviridae SS Enveloped Picornaviridae Astroviridae Caliciviridae Reoviridae SS SS SS DS segmented Naked Icosahedral
  23. 23. GENERAL PRINCIPLES <ul><li>DNA VIRUSES: </li></ul><ul><li>Double stranded DNA except Parvovirus </li></ul><ul><li>Naked except Herpes, Hepadna & Poxviruses </li></ul><ul><li>Icosahedral symmetry except Poxviruses </li></ul><ul><li>Replicate in the nucleus except Poxviruses </li></ul>
  24. 24. <ul><li>RNA VIRUSES : </li></ul><ul><li>Single stranded RNA except Reovirus </li></ul><ul><li>Enveloped except Reovirus & Picornavirus </li></ul><ul><li>Helical symmetry except Reovirus, Picornavirus & Togavirus </li></ul><ul><li>Replicate in the cytoplasm except Orthomyxovirus & retroviruses </li></ul>
  25. 25. THANK YOU

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