International Committee on Taxonomy of Viruses (ICTV) is a universal system for classifying viruses and a unified taxonomy established since 1966. The system makes use of a series of ranked taxons, with the:Family (-viridae)
Subfamily (-virinae)
Classification criteria include:
- Nature of genome and sequence relations
- Virus structure
- Natural host range
- Cell and tissue tropism
- Pathogenicity and cytopathology
- Mode of transmission
- Physicochemical properties of virions
- Antigenic properties of viral proteins
Five orders have been established by the ICTV:Caudovirales, Herpesvirales, Mononegavirales, Nidovirales, and Picornavirales. These orders span viruses with varying host ranges.
- Caudovirales: tailed dsDNA (group I) bacteriophages
- Herpesvirales: large eukaryotic dsDNA viruses
- Mononegavirales: non-segmented (-) strand ssRNA (Group V) plant and animal viruses
- Nidovirales :(+) strand ssRNA (Group IV) viruses with vertebrate hosts
- Picornavirales: small (+) strand ssRNA viruses that infect a variety of plant, insect, and animal hosts.
In ICTV, a minor point is that names of orders and families are italicized. Most notably, type species names generally take the form of [Disease] virus. The establishment of an order is based on the inference that the virus families contained within a single order have most likely evolved from a common ancestor. The majority of virus families remain unplaced. Currently (2008) 82 families and 2,083 species of virus have been defined. Not all viruses are assigned nomenclature accordingly yet.
How do we use this method?
E.g. 1. Ebolavirus
- Order Mononegavirales
- Family Filoviridae
- Genus Filovirus
- Type species: Ebola virus Zaire
E.g. 2. Herpesvirus
-No order assigned
-Family Herpesviridae
-Subfamily Alphaherpesviridae
-Genus Simplexvirus
-Type species: Human herpes virus 1