Classification of Virus

• Viruses


  Composed of protein and nucleic acid, lack metabolism and replicate only in host cells
• Viroids


  Non-translated ssRNAs, lack protein (Infect plants)
• Satellites


  Subviral infectious agents composed of nuclei acid and protein that require a helper virus to replicate
• Prions


  Infectious proteins, cause Spongiform encephalopathies (mad cow disease, scrapie, CJD)
• Serology


  The ability of antibodies to recognise the virus
• Baltimore classification


  Classifies viruses based on virus genome type and replication strategy
• Regardless of their hosts, all viruses must undergo each of these stages in some form to successfully complete their replication cycles. Baltimore classification classifies on genome type and replication strategy
• Class I: DS DNA VIRUSES

  • Genomes are typically large dsDNA molecules that can be over 200,000 base pairs in length (200 Kb)
  • Members include Herpesviruses and Poxviruses
  • Most dsDNA viruses replicate in the host cell nucleus, some replicate in the cytoplasm

  
• DNA bacteriophages and poxviruses replicate in the cytoplasm not the in the nucleus
• Class II: SS DNA Viruses

  • Genome contains only one strand of DNA
  • ssDNA viruses include viruses that infect: bacteria (“bacteriophages”, eg. Inoviridae, Microviridae)
  • Mammals (Circoviridae, Parvoviridae)
  • Plants (Geminiviridae)
• Class III: DS RNA Viruses

  • Genome is composed of two strands of complementary RNA annealed together as with the dsDNA viruses
  • Examples of this class can infect: