The order Nidovirales comprises four families of viruses with a non-segmented, single-stranded RNA genome of positive polarity . The name derives from the Latin nidus from (Nest), which (Engl. The nested nested ) messenger RNAs of Nidovirales alludes. The three families of nidovirales differ from all other RNA viruses in terms of the structure and function of the viral replicase ( RNA polymerase ). Based on structural investigations of these replicases, it was initially referred to as a “ coronavirus-like superfamily ”. This is the reason why other families were not grouped together in one order.
The representatives of the Nidovirales cause important infections in mammals (especially the Coronaviridae family ). Only the Roniviridae family is found only in crustaceans .
The nidovirales have comparatively large RNA genomes from 13-16 kb ( arterivirus ) to 28-31 kb ( Coronaviridae ). This subfamily also includes the virus with the largest known non-segmented RNA genome to date, the mouse hepatitis virus (MHV) with a size of 31,526 nt . The genomic RNA of the nidovirales is polyadenylated and has (except for the genus Okavirus ) a cap structure at its 5 'end. The strategy of nidovirales in the transcription of the viral mRNAs is typical . The different transcripts of at least one reading frame have the same polyA end but different starting points, so they are polycistronic ( nested ) mRNAs.
Systematics
According to the ICTV as of March 2020, the nidovirales are structured as follows:
AMQ King, MJ Adams, EB Carstens, EJ Lefkowitz (Eds.): Virus Taxonomy. Ninth Report of the International Committee on Taxonomy of Viruses. Amsterdam 2012 ISBN 978-0-12-384684-6 , pp. 785-795
CM Fauquet, MA Mayo et al .: Eighth Report of the International Committee on Taxonomy of Viruses , London, San Diego, 2005
David M. Knipe, Peter M. Howley, et al. (Ed.): Fields' Virology, 4th Edition, Philadelphia 2001
↑ OIE: CHAPTER 2.2.9. Infection With Yellow Head Virus Genotype 1 Infection with yellow head virus genotype 1 means infection with the pathogenic agent yellow head virus genotype 1 (YHV1) of the Genus Okavirus and Family Roniviridae , in: Manual of Diagnostic Tests for Aquatic Animals, August 19, 2019