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Group 1 , dsDNA viruses – Replicating through DNA
Group 2 , ss DNA viruses- Replicating through DNA
Group 3 , ds RNA viruses- Replicating through RNA
Group 4 , ssRNA viruses (+) polarity, (sense to mRNAs) - Replicating through RNA
Group 5 , ssRNA viruses (-) polarity, (antisense to mRNAs) - Replicating through RNA
Group 6 , RNA-retroid genomes (RNA -> DNA -> RNA) - Replicating using reverse transcriptase having dsDNA as an intermediate.
Group 7 , DNA-retroid genomes (DNA -> RNA -> DNA) - Replicating using reverse transcriptase having ssRNA as an intermediate.
Current virus classification is based mainly on the morphology, nucleic acid type, host organism it infects, replication mode, and the disease type caused. International committee on taxonomy of viruses (ICTV) was established in 1966 in order to establish a universal system for virus classification. In the eighth report of ICTV which was published in 2005, three orders, 73 families, 9 subfamilies, 287 generas and more than 5000 viruses were approved. It is absolutely impossible to be up to date on the numbers that were approved by the ICTV as everyday new viruses are added to the database. The most current information is available in the ICTV webpage (http://www.ictvonline.org/index.asp).
Family - It is defined as a group of genera with common characteristics. It is written as capitalized, Italicized, and ends in - viridae . Examples- Paramyxoviridae , Poxviridae (poxvirus family).
Subfamily - These are groups of viruses within some large families. They are written as capitalized, Italicized, and end with - virinae. Examples- Paramyxovirinae, Parvovirinae, Alphaherpesvirinae.
Genus - It is defined as a group of virus species sharing common characteristics. They are written as capitalized, Italicized, and end with - virus . Examples- Parvovirus , Flavivirus, Coronavirus.
Species - It is defined as a population of strains from one particular source, all of which have a common property that separates them from other strains. While writing the name of the species it is neither capitalized nor italicized. Eg. vaccinia virus, human immunodeficiency virus, influenza A virus.