ICTV

Acronym for International Committee on Taxonomy of Viruses. This committee has developed a classification of viruses on the basis of collected morphological, molecular and biological properties of viruses.

The older Baltimore classification is considered obsolete. This classification was temporarily established based on knowledge of the molecular biology of viruses. It goes back to a proposal made by the Nobel Prize winner David Baltimore in 1971.

The International Committee on Taxonomy of Viruses (ICTV) is charged with the development, refinement, and maintenance of universal virus taxonomy. This task includes classifying virus species and higher-level taxa according to the genetic and biological properties of their members; naming virus taxa; maintaining a database detailing the currently approved taxonomy; and making the database, supporting proposals, and other virus-related information available from a public, open-access website. The ICTV website(http://ictv.global) provides access to the current taxonomy database in online and downloadable formats and maintains a complete history of virustaxa back to the first publication in 1971, with comprehensive descriptions of all virustaxa covering virus structure, genome structure, biology, and phylogenetics. The ninth ICTV report, published in 2012, is available as an open access online publication on the ICTV website. The current, 10th report (http://ictv.global/report/) is published online, replacing the previous hardcopy edition with a fully open, continuously updated publication.

High-throughput sequencing (HTS) and its use in recovering and assembling novel viral sequences from environmental, clinical, veterinary, and plant samples have uncovered a vast new catalog of viruses (Lefkowitz EJ et al. 2018). Their classification, known by their sequences alone, poses a major challenge to traditional virus taxonomy, particularly at the family and species levels, which have historically been largely based on descriptive taxon definitions. These typically include some knowledge of their phenotypic properties, including replication strategies, virion structure, and clinical and epidemiological features such as host range, geographic distribution, and disease outcomes. However, for viruses identified in metagenomic datasets, little to no information is available. If such viruses are to be included in virus taxonomy, their assignments must be guided largely or entirely by metrics of genetic relatedness. The immediate problem with this is that the International Committee on Taxonomy of Viruses (ICTV), an organization that approves the taxonomic classification of viruses, provides little or no guidance on how similar or how different viruses must be to be considered members of new species or new families. A rapid and objective means to explore metagenomic viral diversity and make evidence-based assignments for such viruses at each taxonomic layer is essential. Sequence analysis can provide evidence that family assignments (and genera) of currently classified viruses are largely underpinned by genomic relatedness, and these features could guide evidence-based classification of metagenomic viruses in the future (Simmonds P et al. (2018).

1. Simmonds P et al (2018) Virus classification - where do you draw the line? Arch Virol 163:2037-2046.
2. Lefkowitz EJ et al. (2018) Virus taxonomy: the database of the International Committee on Taxonomy of Viruses (ICTV). Nucleic Acids Res 46: D708-D717.