Coronaviruses: modern taxonomy and research chronology
Abstract
The classification of coronaviruses began in 1968 when five viruses (IBV, MHV, B814, 229E, and OC43) were united into an independent group, “coronaviruses”, based on the characteristic morphology of the virions. In 1971, the genus Coronavirus was formed, and in 1975, the family Coronaviridae, which in 1996 was included in the order Nidovirales. In 2009, the Coronaviridae family was divided into subfamilies. In 2018, new taxa of viruses were created – region, suborder, and subgenus, and in 2019 – kingdom, type, and class. According to the International Committee on Taxonomy of Viruses, issue No. 37 of 07.2021 (ratification of 03.2022), the family Coronaviridae belongs to the region Riboviria, kingdom Orthornavirae, phylum Pisuviricota, class Pisoniviricetes, order Nidovirales, suborder Cornidovirineae. The Coronaviridae family includes 54 viruses, which are grouped into three subfamilies (Letovirinae, Orthocoronavirinae, Pitovirinae), six genera (Alphaletovirus, Alphacoronavirus, Betacoronavirus, Deltacoronavirus, Gammacoronavirus, Alphapironavirus) and 28 subgenera. Representatives of the most numerous subfamily Orthocoronavirinae infect various species of mammals and birds, causing various pathologies: respiratory and intestinal infections, polyserositis, myocarditis, hepatitis, nephritis, neuroinfections, immunopathology. In particular, viruses that cause infectious bronchitis in chickens, transmissible gastroenteritis in pigs, epidemic diarrhea in pigs, encephalomyelitis in pigs, coronavirus infection in cattle, and epizootic catarrhal gastroenteritis in minks are relevant for veterinary practice. The natural reservoirs of coronaviruses from the genera Alphacoronavirus and Betacoronavirus are bats and birds from the genera Gammacoronavirus and Deltacoronavirus. Particularly dangerous human coronaviruses are SARS-CoV, MERS-CoV and SARS-CoV-2, which cause emergent infections. The circulation of SARS-CoV, MERS-CoV, and SARS-CoV-2 among animals is shown. The natural reservoir of these viruses is bats, and the intermediate hosts for SARS-CoV are Himalayan civets, one-humped camels for MERS-CoV, and pangolins for SARS-CoV-2. The circulation of SARS-CoV-2 among different species of domestic and wild animals leads to the accumulation of mutations, which causes the adaptation of the virus to new hosts and ecological niches and its subsequent introduction into the human population.
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