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Corrigendum: Updated classification of norovirus genogroups and genotypes
ICTV Virus Taxonomy Profile: Caliciviridae
The family Caliciviridae includes viruses with single-stranded positive-sense RNA genomes of 7.4–8.3 kb. The most clinically important representatives are human noroviruses which are a leading cause of acute gastroenteritis in humans. Virions are non-enveloped with icosahedral symmetry. Members of seven genera infect mammals (Lagovirus Norovirus Nebovirus Recovirus Sapovirus Valovirus and Vesivirus) members of two genera infect birds (Bavovirus and Nacovirus) and members of two genera infect fish (Minovirus and Salovirus). This is a summary of the International Committee on Taxonomy of Viruses (ICTV) Report on the family Caliciviridae which is available at ictv.global/report/caliciviridae.
Updated classification of norovirus genogroups and genotypes
Noroviruses are genetically diverse RNA viruses associated with acute gastroenteritis in mammalian hosts. Phylogenetically they can be segregated into different genogroups as well as P (polymerase)-groups and further into genotypes and P-types based on amino acid diversity of the complete VP1 gene and nucleotide diversity of the RNA-dependent RNA polymerase (RdRp) region of ORF1 respectively. In recent years several new noroviruses have been reported that warrant an update of the existing classification scheme. Using previously described 2× standard deviation (sd) criteria to group sequences into separate clusters we expanded the number of genogroups to 10 (GI-GX) and the number of genotypes to 49 (9 GI 27 GII 3 GIII 2 GIV 2 GV 2 GVI and 1 genotype each for GVII GVIII GIX [formerly GII.15] and GX). Viruses for which currently only one sequence is available in public databases were classified into tentative new genogroups (GNA1 and GNA2) and genotypes (GII.NA1 GII.NA2 and GIV.NA1) with their definitive assignment awaiting additional related sequences. Based on nucleotide diversity in the RdRp region noroviruses can be divided into 60 P-types (14 GI 37 GII 2 GIII 1 GIV 2 GV 2 GVI 1 GVII and 1 GX) 2 tentative P-groups and 14 tentative P-types. Future classification and nomenclature updates will be based on complete genome sequences and will be coordinated and disseminated by the international norovirus classification-working group.
Norovirus recombination
RNA recombination is a significant driving force in viral evolution. Increased awareness of recombination within the genus Norovirus of the family Calicivirus has led to a rise in the identification of norovirus (NoV) recombinants and they are now reported at high frequency. Currently there is no classification system for recombinant NoVs and a widely accepted recombinant genotyping system is still needed. Consequently there is duplication in reporting of novel recombinants. This has led to difficulties in defining the number and types of recombinants in circulation. In this study 120 NoV nucleotide sequences were compiled from the current GenBank database and published literature. NoV recombinants and their recombination breakpoints were identified using three methods: phylogenetic analysis SimPlot analysis and the maximum χ 2 method. A total of 20 NoV recombinant types were identified in circulation worldwide. The recombination point is the ORF1/2 overlap in all isolates except one which demonstrated a double recombination event within the polymerase region.