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Transmission electron micrograph of Avian coronavirus
Illustration of a SARS-CoV-2 virion
Illustration of a SARS-CoV-2 virion[2]
  Red: spike proteins (S)
  Yellow: envelope proteins (E)
  Orange: membrane proteins (M)
Virus classification Edit this classification
(unranked): Virus
Realm: incertae sedis
Kingdom: incertae sedis
Phylum: incertae sedis
Class: incertae sedis
Order: Nidovirales
Family: Coronaviridae
Subfamily: Orthocoronavirinae
  • Coronavirinae

Coronaviruses are a group of RNA viruses.[5][6] They cause diseases in birds and mammals, including humans. These diseases can be mild, or they can be fatal. In humans and birds, they cause respiratory tract infections. Mild illnesses in humans include some cases of the common cold (which is also caused by other viruses, for example rhinoviruses). More lethal varieties can cause SARS, MERS, and COVID-19.

They are enveloped viruses with a positive-sense RNA genome.[7] The genome size of coronaviruses is about 26 to 32 kilobases,[8] which is extraordinarily large for an RNA virus. There are four major groups of coronaviruses, called alpha, beta, gamma, and delta.

The most famous coronavirus is one of the betas, the kind that causes Coronavirus disease 2019 (COVID-19) in humans.

The name "coronavirus" comes from the Latin word corona, meaning "crown" or "halo", and refers to how virions look under an electron microscopy (E.M.).[9] They have a fringe of large, bulbous surface projections looking like a crown. This morphology is created by the viral spike (S) peplomer, which are proteins on the surface of the virus. They decide which cells the virus can infect.

Proteins of coronaviruses are the spike (S), envelope (E), membrane (M), and nucleocapsid (N).

Diseases[change | change source]

Coronaviruses infect the upper respiratory and gastrointestinal tracts of mammals and birds. Six different strains of coronaviruses infect humans. These include:

Coronaviruses are believed to cause many common colds in human adults. The significance and economic impact of coronaviruses is hard to assess. Unlike rhinoviruses (another common cold virus), human coronaviruses are easy to grow in the laboratory.

Structure[change | change source]

Structure of a coronavirus

Coronaviruses are large, spherical particles with unique surface projections.[10] Their size is variable, averageing 80 to 120 nms.[11] The total molecular weight is on average 40,000 kDa. They are enclosed in an envelope studded with projecting protein molecules.[12] These layers protect the virus when it is outside the host cell.[13]

The viral envelope is made up of a lipid bilayer in which the membrane (M), envelope (E), and spike (S) structural proteins are anchored.[14] The ratio of E:S:M in the lipid bilayer is approximately 1:20:300.[15] The E and M protein are the structural proteins that combined with the lipid bilayer to shape the viral envelope and maintain its size. S proteins are needed for interaction with the host cells. But human coronavirus NL63 is peculiar in that its M protein has the binding site for the host cell, and not its S protein.[16] The diameter of the envelope is 85 nm.

History[change | change source]

The earliest reports of a coronavirus infection in animals occurred in the late 1920s, when an acute respiratory infection of domesticated chickens happened in North America.[17] Arthur Schalk and M.C. Hawn in 1931 made the first detailed report which described a new respiratory infection of chickens in North Dakota. It was not realized at the time that three related viruses were involved.[18]

Human coronaviruses were discovered in the 1960's using two different methods.[19][20][21] E.C. Kendall, Malcolm Bynoe, and David Tyrrel, working at the Common Cold Unit of the British Medical Research Council, collected a unique common cold virus B814 in 1961.[22][23][24] The virus could not be cultivated using the techniques which had successfully cultivated rhinoviruses, adenoviruses, and other known common cold viruses. Eventually, this was solved.[25] The new cultivating method was introduced to the lab by Bertil Hoorn.[26] The isolated virus, when put into the noses of volunteers, caused a cold. The virus was inactivated by ether which showed it had a lipid envelope.[22][27][28] The novel virus caused a cold in volunteers and, like B814, was inactivated by ether.[29]

Transmission electron micrograph of organ cultured coronavirus OC43

Scottish virologist June Almeida at St Thomas' Hospital, London, compared the structures of IBV, B814, and 229E in 1967.[30][31] Using transmission electron microscopy,the three viruses were shown to be similar in shape and have club-like spikes.[32] A research group at the National Institute of Health the same year isolated another member of this group of viruses.[33] Like B814, 229E, and IBV, the novel cold virus OC43 had distinctive club-like spikes when observed with the electron microscope.[34][35]

The IBV-like novel cold viruses looked like the mouse hepatitis virus. This new group of viruses were called "coronaviruses" from their crown-like appearance.[36][37] The coronavirus strain B814 was lost. It is not known which present human coronavirus it was.[38] Other human coronaviruses have since been identified, including SARS-CoV in 2003, HCoV NL63 in 2003, HCoV HKU1 in 2004, MERS-CoV in 2013, and SARS-CoV-2 in 2019.[39] There have been a large number of animal coronaviruses identified since the 1960s.

Related pages[change | change source]

References[change | change source]

  1. "Virus Taxonomy: 2018b Release". International Committee on Taxonomy of Viruses (ICTV). March 2019. Archived from the original on 4 March 2018. Retrieved 24 January 2020.
  2. Giaimo C (1 April 2020). "The Spiky Blob Seen Around the World". The New York Times. Archived from the original on 2 April 2020. Retrieved 6 April 2020.
  3. "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.
  4. "ICTV Taxonomy history: Orthocoronavirinae". International Committee on Taxonomy of Viruses (ICTV). Retrieved 24 January 2020.
  5. de Groot R.J. (2012). "Family Coronaviridae". In King A.M.Q. ' (ed.). Ninth Report of the International Committee on Taxonomy of Viruses. Elsevier, Oxford. pp. 806–828. ISBN 978-0-12-384684-6.
  6. International Committee on Taxonomy of Viruses. "ICTV Master Species List 2009 – v10" (xls).
  7. enveloped = has viral envelopes covering their protective protein capsids; positive sense = the RNA sequence may be directly translated into the desired viral proteins.
  8. One kilobase = 1000 base pairs
  9. virion = complete virus particle.
  10. Goldsmith CS, Tatti KM, Ksiazek TG, Rollin PE, Comer JA, Lee WW, et al. (February 2004). "Ultrastructural characterization of SARS coronavirus". Emerging Infectious Diseases. 10 (2): 320–6. doi:10.3201/eid1002.030913. PMC 3322934. PMID 15030705. Virions acquired an envelope by budding into the cisternae and formed mostly spherical, sometimes pleomorphic, particles that averaged 78 nm in diameter (Figure 1A).
  11. Masters PS (2006). "The molecular biology of coronaviruses". Advances in Virus Research. 66: 193–292. doi:10.1016/S0065-3527(06)66005-3. ISBN 9780120398690. PMC 7112330. PMID 16877062.
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  14. Lai MM, Cavanagh D (1997). "The molecular biology of coronaviruses". Advances in Virus Research. 48: 1–100. doi:10.1016/S0065-3527(08)60286-9. ISBN 9780120398485. PMC 7130985. PMID 9233431.
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  22. 22.0 22.1 Kendall EJ, Bynoe ML, Tyrrell DA (July 1962). "Virus isolations from common colds occurring in a residential school". British Medical Journal. 2 (5297): 82–6. doi:10.1136/bmj.2.5297.82. PMC 1925312. PMID 14455113.
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  33. McIntosh K, Becker WB, Chanock RM (December 1967). "Growth in suckling-mouse brain of "IBV-like" viruses from patients with upper respiratory tract disease". Proceedings of the National Academy of Sciences of the United States of America. 58 (6): 2268–73. Bibcode:1967PNAS...58.2268M. doi:10.1073/pnas.58.6.2268. PMC 223830. PMID 4298953.
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  35. Times, Harold M. Schmeck Jr Special To the New York (1967-05-05). "Six newly discovered viruses may explain cold: strains are similar to germ that causes a bronchial infection in chickens believed to be new group". The New York Times. ISSN 0362-4331. Retrieved 2020-04-25.
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  38. Corman VM, Jores J, Meyer B, Younan M, Liljander A, Said MY, et al. (August 2014). "Coronaviruses". Viral Infections of Humans. Vol. 20. pp. 1319–22. doi:10.1007/978-1-4899-7448-8_10. ISBN 978-1-4899-7447-1. PMC 7122465. PMID 25075637. The other OC strains and B814 that could not be adapted to mouse brain resisted adaptation to cell culture as well; these distinct viruses have since been lost and may actually have been rediscovered recently. {{cite book}}: |journal= ignored (help)
  39. Zhu N, Zhang D, Wang W, Li X, Yang B, Song J, et al. (February 2020). "A Novel Coronavirus from Patients with Pneumonia in China, 2019". The New England Journal of Medicine. 382 (8): 727–733. doi:10.1056/NEJMoa2001017. PMC 7092803. PMID 31978945.