ICTV Virus Taxonomy Profile: Coronaviridae 2023

1Orthocoronavirus virions are enveloped, pleomorphic and roughly spherical viral particles with surface projections of the spike (S) protein; the family name derives from electron micrograph images which are reminiscent of the solar corona. The nucleocapsid, comprising nucleocapsid protein (N) and RNA, appears to be loosely wound, with small helical units distributed throughout the virion interior. Virions consist of three or four membrane-associated proteins: spike (S), envelope (E) and membrane (M) glycoprotein (Table 1, Fig. 1). A haemagglutinin-esterase (HE) glycoprotein is only present in members of the subgenus Embecovirus in the genus Betacoronavirus.

2The coronavirus genome is a linear, positive-sense RNA of 22–36 kb with a 5′-cap structure and a 3′-polyadenylated tail and a typical genome organization of 5′-NCR-replicase-S-E-M-N-NCR-3′. The replicase gene comprises two large overlapping ORFs, 1a and 1b. Translation of ORF1b is programmed by −1 ribosomal frameshifting and produces polyproteins pp1a and pp1ab, which are further processed by virus-encoded proteinases. Genes for the structural proteins S, E, M and N are interspersed with a variable number of accessory protein ORFs (Fig. 2).

3Coronavirus replication takes place in the cytoplasm. The viral genome serves as a template for synthesizing genomic-size negative-sense RNA for replication and subgenomic-size negative-sense RNA molecules that template the production of subgenomic mRNAs. The 3′-proximal viral genes are expressed from a nested set of 3′-coterminal subgenomic mRNAs generated by the fusion of coding sequences to common 5′-leader sequences by a mechanism of discontinuous transcription.

4Coronaviruses infect a wide range of animals including humans. Clinical manifestations range from asymptomatic to fatal diseases. Nine coronaviruses that infect humans have been identified so far, including four human seasonal coronaviruses (human coronavirus OC43, human coronavirus 229E, human coronavirus NL63, human coronavirus HKU1), canine coronavirus, porcine coronavirus HKU15 (also known as porcine deltacoronavirus), severe acute respiratory syndrome coronavirus, severe acute respiratory syndrome coronavirus 2 and Middle East respiratory syndrome-related coronavirus.

5Current taxonomy: ictv.global/taxonomy. In the subfamily Orthocoronavirinae, members of the genera Alphacoronavirus and Betacoronavirus infect mammals, especially bats; members of the genera Gammacoronavirus and Deltacoronavirus primarily infect birds, but also mammals. Hosts for members of the subfamilies Letovirinae and Pitovirinae are amphibians and bony fish, respectively.

6Full ICTV Report on the family Coronaviridae: ictv.global/report/coronaviridae.