Virus Classification

Viruses only show biological activity inside of their host cell and is inactive outside the cell.
Classification of viruses are based on its natural properties and resultant properties.

There are 3 types of classifications. They are Lwoff's Scheme for Classification, Baltimore's System for Classification and ICTV Classification.

Lwoff's Scheme for Classification
Lwoff, RW horne and P Tournier were the founder of this classification.

Classification is based on shared properties. It is based on

• Nucleic acid of the Virus
  
• Symmetry of capsid
  
• Enveloped or naked
  
• Size of Virion and capsid

Baltimore's System for Classification
David Baltimore was the founder of this classification.

Classification is based on

• Viral genome
  
• Viral genome relationship to mRNA

• Central dogma of molecular biology

Viruses can be placed into 1 of the 7 groups:

1. Group I - dsDNA viruses
   
2. Group II - ssDNA viruses
   
3. Group III - dsRNA viruses
   
4. Group IV - positive-sense ssRNA viruses
   
5. Group V - negative-sense ssRNA viruses
   
6. Group VI - RNA reverse transcribing viruses
   
7. Group VII - DNA reverse transcribing viruses

http://en.wikipedia.org/wiki/File:Baltimore_Classification.png

ICTV Classification

- International Commitee on Taxonomy of Viruses

This Classification is based on the Lwoff's scheme and Baltimore's Classification. It is the current classification system.

The Classification Criteria are

• Nature of genome and sequence relatedness


• Virus structure


• Natural host range


• Cell and tissue tropism


• Pathogenicity and cytopathology


• Mode of transmission


• Physicochemcial properties of virions


• Antigenic properties of viral proteins

Taxonomy of Virus are

Order (virales), Family (viridae), Subfamily (virinae), Genus (virus) and Species (virus)

http://www.ncbi.nlm.nih.gov/ICTVdb/Images/virosphere05.htm