The viral genome is 26–32 kilobases in length. The particles are typically decorated with large (~20 nm), club- or petal-shaped surface projections (the "peplomers" or "spikes"), which in electron micrographs of spherical particles create an image reminiscent of the solar corona.[1][2][3]
Genetic recombination can occur when at least two viral genomes are present in the same infected host cell. RNA recombination appears to be a major driving force in coronavirus evolution. Recombination can determine genetic variability within a CoV species, the capability of a CoV species to jump from one host to another and, infrequently, the emergence of a novel CoV.[6] The exact mechanism of recombination in CoVs is not known, but likely involves template switching during genome replication.[6]
Taxonomy
The family Coronaviridae is organized in 2 sub-families, 5 genera, 26 sub-genera, and 46 species.[7] Additional species are pending or tentative.[8]
Coronavirus is the common name for Coronaviridae and Orthocoronavirinae, also called Coronavirinae.[10][11] Coronaviruses cause diseases in mammals and birds. In humans, the viruses cause respiratory infections. Four human coronaviruses cause typically minor symptoms of a common cold, while three are known to cause more serious illness and can be lethal: SARS-CoV-1, which causes SARS; MERS-CoV, which causes MERS; and SARS-CoV-2, which causes COVID-19.[12] Symptoms vary in other species: in chickens, they cause an upper respiratory disease, while in cows and pigs coronaviruses cause diarrhea. Other than for SARS-CoV-2, there are no vaccines or antiviral drugs to prevent or treat human coronavirus infections. They are enveloped viruses with a positive-sense single-strandedRNAgenome and a nucleocapsid of helical symmetry. The genome size of coronaviruses ranges from approximately 26 to 32 kilobases, among the largest for an RNA virus (second only to a 41-kb nidovirus recently discovered in planaria).[13]
^Alfarouk, Khalid O.; AlHoufie, Sari T. S.; Ahmed, Samrein B. M.; Shabana, Mona; Ahmed, Ahmed; Alqahtani, Saad S.; Alqahtani, Ali S.; Alqahtani, Ali M.; Ramadan, AbdelRahman M.; Ahmed, Mohamed E.; Ali, Heyam S.; Bashir, Adil; Devesa, Jesus; Cardone, Rosa A.; Ibrahim, Muntaser E.; Schwartz, Laurent; Reshkin, Stephan J. (21 May 2021). "Pathogenesis and Management of COVID-19". Journal of Xenobiotics. 11 (2): 77–93. doi:10.3390/jox11020006. PMC8163157. PMID34063739.
^ abSu S, Wong G, Shi W, Liu J, Lai ACK, Zhou J, Liu W, Bi Y, Gao GF. Epidemiology, Genetic Recombination, and Pathogenesis of Coronaviruses. Trends Microbiol. 2016 Jun;24(6):490-502. DOI: 10.1016/j.tim.2016.03.003. Epub 2016 Mar 21. Review. PMID27012512
^"Virus Taxonomy: 2019 Release". talk.ictvonline.org. International Committee on Taxonomy of Viruses. Retrieved 11 May 2020.
^"2017.012-015S"(xlsx). International Committee on Taxonomy of Viruses (ICTV). October 2018. Archived from the original on 14 May 2019. Retrieved 24 January 2020.