1. VIRUS CLASSIFICATION By

2. Criteria for Classification Virus classification involves naming and placing viruses into a taxonomic system. Virus classification is based mainly on phenotypic characteristics, including morphology, nucleic acid type, mode of replication, host organisms, and the type of disease they cause.

3. Classification Systems Combination of two main schemes is currently used for the classification of viruses. Baltimore classification system: viruses into seven groups based on their mode of replication and genome type. ICTV classification system: based on naming conventions and further classification guidelines

4. Baltimore Classification System Viruses are placed in one of the seven following groups: Group I: double-stranded DNA viruses e.g. Herpesviridae � HSV 1 & 2, EBV Group II: single-stranded DNA viruses e.g. Parvoviridae � Parvovirus B19 Group III: double-stranded RNA viruses e.g. Reoviridae - Rotavirus Group IV: positive-sense single-stranded RNA viruses e.g. Picornaviridae � Poliovirus, Hepatitis A virus; Coronaviridae - SARS Group V: negative-sense single-stranded RNA viruses e.g. Paramyxoviridae � Measles virus; Filoviridae � Ebola virus Group VI: reverse transcribing Diploid single-stranded RNA viruses e.g. Retroviridae � HIV, HTLV 1 & 2 Group VII: reverse transcribing Circular double-stranded DNA viruses e.g. Hepadnaviridae � Hepatitis B virus

5. ICTV Classification System Viral classification starts at the level of order and follows as thus, with the taxon suffixes given in italics: Order (-virales) Family (-viridae) Subfamily (-virinae) Genus (-virus) Species (-virus)? Names of orders and families are italicized. Species names generally take the form of [Disease] Virus. Recognition of orders very recent and deliberately slow; to date, only three have been named, and most families remain unplaced. Approximately 80 families and 4000 species of virus are known.