Coronaviruses

Human Coronaviruses (HCoVs)

Human coronaviruses (HCoVs) belong to order Nidovirales, family Coronaviridae, subfamily Coronavirinae, and either genus Alphacoronavirus or Betacoronavirus. HCoVs have been found in the 1960s in the noses of people with the common cold, which represent a major group of coronaviruses (CoVs) associated with multiple respiratory diseases of varying severity, including common cold, pneumonia and bronchiolitis ^[1]. They typically cause transient respiratory or gastrointestinal illness.

To date, seven known HCoVs have been identified, namely HCoV-229E, HCoV-NL63, HCoV-OC43, HCoV-HKU1, severe acute respiratory syndrome coronavirus (SARS-CoV), Middle East respiratory syndrome coronavirus (MERS-CoV) and 2019 Novel Coronavirus (SARS-CoV-2).

Of which, four HCoVs (HCoV-229E, HCoV-NL63, HCoV-OC43 and HCoV-HKU1) are globally circulated in the human population and contribute to approximately one-third of common cold infections in humans ^[2].

Transmission of HCoVs

HCoVs can spread from one person to the next, scientists believe that the viruses transmit via fluids in the respiratory system, such as mucus. Coronaviruses can spread in the following ways:

• The air by coughing and sneezing
• Close personal contact, like touching or shaking hands
• Touching an object or surface with the virus on it, then touching your mouth, nose, or eyes before washing your hands

Diseases Caused by HCoVs

Human coronaviruses are typically responsible for common colds more than serious diseases. However, coronaviruses are also behind some more severe outbreaks such as severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS) and COVID-19.

SARS

SARS is a viral respiratory illness caused by a coronavirus, called SARS-associated coronavirus (SARS-CoV). Typically, it leads to a life threatening form of pneumonia. SARS was first reported in Asia in November 2002. Over the next few months, the illness spread to more than two dozen countries in North America, South America, Europe, and Asia before the SARS global outbreak of 2003 was contained ^[3].

According to the World Health Organization (WHO), a total of 8,098 people worldwide became sick with SARS during its outbreak. Of these, 774 infections were fatal. This equates to a mortality rate of 9.6%.

The symptoms of SARS develop over the course of a week and start with a fever. Early on in the condition, people develop flu-like symptoms, such as dry coughing, chills, diarrhea, breathlessness and aches. Pneumonia, a severe lung infection, usually develops. At its most advanced stage, SARS causes failure of the lungs, heart, or liver.

MERS

MERS spreads due to the coronavirus known as MERS-CoV. Scientists first recognized this severe respiratory illness in 2012 after it surfaced in Saudi Arabia. Since then, it has spread to other countries. MERS-CoV caused similar clinical symptoms as SARS-CoV but with a much higher mortality rate of about 35% ^[4].

Symptoms of MERS include fever, breathlessness, and coughing. The illness spreads through close contact with people who already have an infection. However, all cases of MERS have links to individuals recently returning from travel to the Arabian Peninsula.

COVID-19

In 2019, the Centers for Disease Control and Prevention (CDC) started monitoring the outbreak of a new coronavirus, SARS-CoV-2, which causes the respiratory illness now known as COVID-19. Symptoms vary from person-to-person with COVID-19. It may produce few or no symptoms. However, it can also lead to severe illness and may be fatal. Common symptoms include fever, breathlessness and cough. More information about COVID-19, please read 2019 Novel Coronavirus.

Coronavirus Host Cell Receptors

CoV infection is initiated by the attachment to specific host cellular receptors via the spike (S) protein. The host receptor is a major determinant of pathogenicity, tissue tropism and host range of the virus ^[5].

Today, the main host cell receptors utilised by all HCoVs are known: aminopeptidase N by HCoV-229E ^[6], angiotensin-converting enzyme 2 (ACE2) by SARS-CoV ^[7], HCoV-NL63 ^[8] and SARS-CoV-2 ^[9], dipeptidyl peptidase 4 (DPP4) by MERS-CoV ^[10] and 9-O-acetylated sialic acid by HCoV-OC43 and HCoV-HKU1.

References

[1] Pene F, Merlat A, Vabret A, et al. Coronavirus 229E-Related Pneumonia in Immunocompromised Patients [J]. Clin Infect Dis, 2003.

[2] Van der Hoek, L. Human coronaviruses: What do they cause? [J]. Antivir Ther, 2007.

[3] Graham R.L, Donaldson E.F, Baric R.S, et al. A decade after SARS: Strategies for controlling emerging coronaviruses [J]. Nat Rev Microbiol, 2013.

[4] Al Awaidy S. T, Khamis F. Middle East respiratory syndrome coronavirus (MERS-CoV) in Oman: Current situation and going forward [J]. Oman Med J. 2019

[5] Lim Y. X., et al. (2016). Human coronaviruses: A review of virus-host interactions [J]. Diseases, 2016.

[6] Yeager C.L, Ashmun R.A, Williams R.K, et al. Human aminopeptidase N is a receptor for human coronavirus 229E. Nature, 1992.

[7] Li W, Moore M.J, Vasilieva N, et al. Angiotensin-converting enzyme 2 is a functional receptor for the SARS coronavirus. Nature, 2003.

[8] Li W, Sui J, Huang I.C, et al. The S proteins of human coronavirus NL63 and severe acute respiratory syndrome coronavirus bind overlapping regions of ACE2. Virology, 2007.

[9] View ORCID ProfileMarkus Hoffmann, Hannah Kleine-Weber, et al. The novel coronavirus 2019 (2019-nCoV) uses the SARS-coronavirus receptor ACE2 and the cellular protease TMPRSS2 for entry into target cells [J]. bioRxiv. 2020.

[10] Van Doremalen, N, Miazgowicz, K.L, Milne-Price, S, et al. Host Species Restriction of Middle East Respiratory Syndrome Coronavirus through Its Receptor, Dipeptidyl Peptidase 4 [J]. J. Virol. 2014.