Classification of taxonomy - General Virology | BSCI 437, Study notes of Virology

Download Classification of taxonomy - General Virology | BSCI 437 and more Study notes Virology in PDF only on Docsity! BSCI437 Lecture 5: Taxonomy Classification/Taxonomy. Excellent reference. http://www.ncbi.nlm.nih.gov/ICTVdb/index.htm Criteria for classification: 1. Disease symptoms 2. Physical structure of the virus particle. 3. Genome composition and structure Classical: 1. Morphology first, 2. followed by grouping according to physical and chemical composition, 3. followed by genetic relatedness. Molecular: Classification is currently moving toward nucleic acid sequence analysis. Classification and Nomenclature: ICTV-International Committee on Taxonomy of Viruses (meets every 4 years). Present totals (2000): 3 orders, 56 families, 9 subfamilies, 233 genera, and 1550 species. Family- A group of genera with common characteristics.  Capitalized, Italicized, and end in -viridae.  Examples-Picornaviridae (picornavirus family is also acceptable), Herpesviridae (herpesvirus family). Subfamilies- Groups within some large families.  Capitalized, Italicized, end in -virinae.  Examples- Alphaherpesvirinae, Betaherpesvirinae, Gammaherpesvirinae. Genus- A group of virus species sharing common characteristics.  Capitalized, Italicized, ends in-virus.  Examples-Rhinovirus, Simplexvirus Species- A cluster of strains from a variety of sources or a population of strains from one particular source, all of which have in common a set pattern of stable properties that separates the cluster from other clusters or strains.  Not capitalized or italicized.  Examples: poliovirus, human immunodeficiency virus. Example with a common virus (herpes simplex virus 1)  Family: Herpesviridae or herpesvirus family;  Subfamily: Alphaherpesvirinae;  Genus: Simplexvirus;  Species: herpes simplex virus 1. Another example: Poliovirus  Family: Picornaviridae or picornavirus family;  Subfamily: None;  Genus: Enterovirus;  Species: poliovirus Further breakdowns not recognized by the ICTV: Strain- different lines of isolates of the same virus. Example: Isolated from different geographical locations. Type- different serotype (different antigenic specificity) of the same virus. Influenza type A or B. There may also be “subtypes” within a particular type. Group- sub-category of species, division often based on genomic sequence similarities or origin. HIV group M (Main), N (Neither M or O), or O (Outlier). There may also be “subgroups” (sometimes called clades) within a particular group (subgroups A-J of group M HIV). Varient-Virus whose phenotype differs from original wild type strain but where the genetic basis for the difference is not known. Origins of some viral names • Picorna: Pico (small) + RNA • Toga: wearing a toga • Corona: wearing a crown • Retro: use retrotransposition • Filo: Look fibrous • Papilloma: infections result in papilla (bumps on skin), e.g. warts • Adeno: infections of respiratory tract • Hepadna: hepatitis + DNA • Herpes: produce scaly (snake skin) lesions • Pox: infections produce pox lesions Special cases: Satellite viruses, Satellite RNAs and Defective Interfering Elements. Consider the world of viruses as an ecological habitat. In such habitats, organisms tend to evolve relationships with one another: mutualistic, commensalistic, symbiotic, and parasitic. Viruses are no different.  Satellite viruses o Viruses with separate genomes that are encapsidated inside viral particles produced by a “helper” virus. o They also rely on the helper virus replicative machinery to replicate their genomes. o Example: the M1 virus of yeast is the satellite, and the L-A virus is the helper. M1 encodes a toxin. The M1 dsRNA genome is encapsidated inside of viral particles produced by L-A, and is replicated by the L-A