The viral genome is 26–32kilobases in length. The particles are typically decorated with large (~20 nm), club- or petal-shaped surface projections (the "peplomers" or "spikes"), which inelectron micrographs of spherical particles create an image reminiscent of thesolar corona.[1][2][3]
Genetic recombination can occur when at least two viralgenomes 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 of familyCoronaviridae with species pathogenic to humans
The familyCoronaviridae is organized in 3 subfamilies, 6 genera, 28 sub-genera, and 54 species.[7] Additional species are pending or tentative.[8] The subfamilies and genera of the family are listed hereafter (-virinae denotes subfamily and -virus denotes genus):[7]
Coronavirus is the common name forOrthocoronavirinae, previously calledCoronavirinae.[10][11] Coronaviruses cause diseases in mammals and birds. In humans, the viruses causerespiratory infections. Four human coronaviruses cause typically minor symptoms of acommon cold, while three are known to cause more serious illness and can be lethal:SARS-CoV-1, which causesSARS;MERS-CoV, which causesMERS; andSARS-CoV-2, which causesCOVID-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 areenveloped viruses with apositive-sense single-strandedRNAgenome and anucleocapsid of helical symmetry. Thegenome size of coronaviruses ranges from approximately 26 to 32kilobases, among the largest for anRNA virus (second only to a 41-kbnidovirus recently discovered inplanaria).[13]
Phylogenetic tree ofCoronaviridae with host species indicated by color
^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.
^"2017.012-015S"(xlsx).International Committee on Taxonomy of Viruses (ICTV). October 2018.Archived from the original on 14 May 2019. Retrieved24 January 2020.
