28 May 2020

Coronaviruses: what are they? And what do we know about them?

Here we present background information on coronaviruses as well as a timeline of the discovery and important developments related to coronaviruses.

What are coronaviruses?

Coronaviruses are RNA viruses that have characteristic club-shaped spikes projecting from their surface. Viewed through an electron microscope, they are said to be reminiscent of the solar corona from which they get their name.

There are 4 distinct genera of coronavirus:

alphacoronavirus, betacoronavirus, gammacoronavirus and deltacoronavirus.

Within the betacoronaviruses, which includes SARS-CoV-2, there are four subgroups, A-D.

Coronavirus family tree

*Source: Patrick C. Y. Woo, Yi Huang, Susanna K. P. Lau, and Kwok-Yung Yuen – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3185738/, CC BY 3.0,*

There are six known species of human coronaviruses, one of which is subdivided into two different strains, making seven different human coronaviruses. Four of these cause generally mild symptoms of the common cold: HCoV-229E, -NL63, -OC43 and -HKU1 continually circulate in the human population causing respiratory infections worldwide.

Human coronavirus OC43 (HCoV-OC43) of the genus β-CoV
Human coronavirus HKU1 (HCoV-HKU1), β-CoV,
Human coronavirus 229E (HCoV-229E), α-CoV
Human coronavirus NL63 (HCoV-NL63), α-CoV

Three strains (two species) produce symptoms that can be severe; all three of these are β-CoV strains:

Middle East respiratory syndrome-related coronavirus (MERS-CoV)
Severe acute respiratory syndrome coronavirus (SARS-CoV)
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)

The coronaviruses that cause disease in chickens, such as avian infectious bronchitis virus (IBV – a gammacoronavirus), and pigs, such as porcine respiratory coronavirus (PRCV – an alphacoronavirus) belong to different genera than the coronaviruses that cause potentially severe disease in humans: MERS-CoV, SARS-CoV and SARS-CoV-2 are all betacoronaviruses (see coronavirus family tree).

Because the avian coronaviruses and COVID-19 belong to two different groups of coronaviruses, it is highly unlikely that avian coronaviruses will infect humans, or vice-versa.

Coronavirus: key events timeline

Infectious bronchitis of chickens first described as a respiratory disease of chickens

1931

Source:
Jane K. A. Cook, M. Jackwood & R. C. Jones (2012) The long view: 40 years of infectious bronchitis research, Avian Pathology, 41:3, 239-250

Viral cause of infectious bronchitis established

1936

Source:

Jane K. A. Cook, M. Jackwood & R. C. Jones (2012) The long view: 40 years of infectious bronchitis research, Avian Pathology, 41:3, 239-250

First coronavirus (HCoV-229E) isolated from humans – initially named B814

1965

Source:

Tyrell, D.A.J. & Bynoe, M.L. (1966) Cultivation of viruses from a high proportion of patients with colds. The Lancet, 287 (7428), 76-77

Almeida and Tyrrell performed electron microscopy on B814 and found particles that resembled the infectious bronchitis virus (IBV) of chickens, widely spaced club-shaped surface projections

1967

Source:

Almeida JD & Tyrrell DA. (1967) The morphology of three previously uncharacterized human respiratory viruses that grow in organ culture. J Gen Virol. 1967 Apr;1(2):175-8.

Tyrrell led virologists working with the human strains and a number of animal viruses: infectious bronchitis virus, mouse hepatitis virus and transmissible gastroenteritis virus of swine. All were demonstrated to be morphologically using electron microscopy

Late 1960s

Source:

McIntosh K, Becker WB, Chanock RM (1967) Growth in suckling-mouse brain of “IBV-like” viruses from patients with upper respiratory tract disease. Proc Natl Acad Sci U S A. 1967 Dec;58(6):2268-73.

Officially accepted as a new genus of viruses, this new group of viruses was named coronavirus -corona referring to the crown-like appearance of the surface projections

1975

Source:

Tyrrell, D.A.J. et al. (1975) Coronaviridae. Intervirology, 5: 76-82

Genome of a coronavirus (IBV) is shown to be a positive single stranded RNA

1977

Source:

Lomniczi, B., & Kennedy, I. (1977). Genome of infectious bronchitis virus. Journal of virology, 24(1), 99–107.

Structure of IBV spike protein determined comprising two glycopolypeptides, S1 and S2

1983

Source:

Cavanagh, D. (1983) Coronavirus IBV: Structural Characterization of the Spike Protein. Journal of General Virology, 64, 2577-2583.

First full genome sequence of a coronavirus (IBV) published

1987

Source:

Boursnell et al. (1987) Completion of the Sequence of the Genome of the Coronavirus Avian Infections Bronchitis. Journal of General Virology, 68, 57-77.

Severe acute respiratory syndrome coronavirus (SARS-CoV) emerged in humans. Most probably originated in bats, was transmitted to palm civets and then to people in wet markets in southern China

November 2002

Source:

Bart L. Haagmans, Albert D.M.E. Osterhaus, in Vaccines for Biodefense and Emerging and Neglected Diseases, 2009

https://www.sciencedirect.com/topics/medicine-and-dentistry/sars-coronavirus

SARS-CoV outbreaks occurred in Hong Kong, Hanoi, Toronto, and Singapore. All could be directly traced back to index patient who acquired the infection in Guangdong and travelled to Hong Kong. 8096 people became ill, and 774 people died in this first SARS epidemic

2003

Source:

Bart L. Haagmans, Albert D.M.E. Osterhaus, in Vaccines for Biodefense and Emerging and Neglected Diseases, 2009

https://www.sciencedirect.com/topics/medicine-and-dentistry/sars-coronavirus

In addition to significant morbidity and mortality, the SARS pandemic resulted in economic costs of an estimated USD 100 billion USD

2003

Source:

Al-Tawfiq, J.A., Zumla, A., Memish, Z.A., 2014. Travel implications of emerging coronaviruses: SARS and MERS-CoV. Travel Med. Infect. Dis. 12 (5), 422–428.

Dozens of new coronaviruses isolated from bats

2005 onwards

Source:

Korsmann, S.N.J. (2012) Virology. Churchill Livingstone.

First known case of MERS identified in Jordan by retrospective investigations

April 2012

Middle East Respiratory Syndrome (MERS) is caused by a coronavirus called Middle East Respiratory Syndrome Coronavirus (MERS-CoV). Most MERS patients developed severe respiratory illness with f fever, cough and shortness of breath; 3 or 4 out of every 10 patients reported with MERS died.