[2] Classifying Viruses

• Unifying trait for all viruses

  Obligate intracellular parasite
• Instead of classifications based on structure or nucleic acids, it is proposed that protein structure should be the basis
• Basis of viral nomenclature:

  1. Disease caused
  2. Place it was first reported
  3. Greek adjectives
  4. Discoverer
  5. How it was thought to be contracted
  6. Host and signs of disease
  7. Codes
  8. No reason
  9. Any combination
• Morphology classification systems:

  
  

  Presence or Absence of Structures

  1. Enveloped
  2. Non-enveloped

  
  

  Symmetry

  1. Helical symmetry
  2. Isometric symmetry
  3. Complex or no symmetry
• Epidemiology-based Classification Systems (DHTMOA):

  1. Disease caused
  2. Host organism
  3. Tropism
  4. Mode of transmission
  5. Origin
  6. Antigenic properties
• Epidemiological Criteria

  1. Enteric viruses
  2. Respiratory viruses
  3. Arboviruses
  4. Oncogenic viruses
• Enteric viruses are ingested via the fecal oral route

  • Ex. poliovirus
• Respiratory viruses transmitted via inhalation or transmission of fomites, replicate in the respiratory tract
• Arboviruses are transmitted by arthropod bites to vertebrate host
• Oncogenic viruses are tumor-forming viruses transmitted by close contact and injection
• Label the ff. figure

  A) Virus type

  B) Geographic origin

  C) Strain number

  D) Year of isolation

  E) Virus subtype

  F) Hemagglutinin

  G) Neuraminidase

  
• Nucleic Acid of Genome Classification:

  1. Type of Genetic material
  2. DNA
  3. ss
  4. ds
  5. RNA
  6. Shape of genetic material (linear, circular)
  7. Other modifications
• Classical System of Cataloging Viruses (Lwoff, Horne and Tournier)

  1. Nature of the nucleic acid (DNA or RNA)
  2. Symmetry of the protein shell (capsid)
  3. Presence of absence of a lipid membrane (envelope)
  4. Dimensions of the virion and capsid
• Baltimore Classification of Viruses:

  1. Class I - dsDNA
  2. Class II - ssDNA
  3. Class III - dsRNA
  4. Class IV - +RNA
  5. Class V - -RNA
  6. Class VI - +RNA (reverse transcribing)
  7. Class VII - dsDNA (reverse transcribing)
• [+] means negative sense DNA is used as template

  [ - ] uses positive sense DNA as template, needs to be replicated into +RNA before being translated
• dsDNA needs to be replicated by DNA polymerase

  ssDNA needs to be replicated to become double stranded

  dsRNA uses RNA polymerase for replication

  ssRNA similar with ssDNA, needs to be replicated to become double stranded
• These are unconventional viruses, infectious agents that lack either one of virus requirements, or require other viruses to infect

  Subviral Agents
• Satellites have a complete virus structure, but depend on coinfection with a helper virus
• Viroids are infectious agents that are just nucleic acids
• Prions are infectious protein molecules not classified by the ICTV
• These are abnormally folded proteins that can cause disease

  Prions
• Among the three subviral agents, which is NOT under ICTV classification?

  a)Prions

  b) Satellites

  c)Viroids

  A
• Label the ff. figure:

  A) I

  B) II

  C) III

  D) IV

  E) V

  F) VI and VII