CORONAVIRUSES – A FAMILY OF VIRUSES

Coronavirus, COVID, COVID-19, ‘Corona’.  These are all terms we wish we’d never have to hear mentioned again. And yet, they don’t seem to be going away anytime soon!

So why not learn what we can about the subject, to better arm ourselves with facts and useful information rather than conspiracy theories.

Interestingly, what you probably didn’t know, is that there are actually hundreds of coronaviruses out there, but only a few pose a risk to humans.  Professor Johnson Mak, Research Leader and infectious diseases specialist at the Institute for Glycomics, takes us through the basics, helping us understand the significance of this seemingly large family of viruses.

What are coronaviruses?

Coronaviruses are a large family of viruses that typically cause mild to moderate upper-respiratory tract infections. Although there are hundreds of coronaviruses, most of them circulate among animals such as bats, pigs, camels and cats.

But we now know all too well that humans can also be infected by coronaviruses; so, at this point you may ask how coronaviruses can ‘jump’ from one species to another species and cause disease. Good question.  This process is known as a ‘spill-over event’.  When a spill-over event occurs with a pathogen from an animal (natural co-existing host) jumping to a human (new host), this process is known as zoonosis.

Understanding ‘spill-over events’

Viruses completely rely on a host to propagate. In the absence of an appropriate host, viruses don’t have access to host cells to cause infection and thus will reach the end of their ‘lives’.

All viruses have their specific host targets, and this phenomenon is known as tropism. Tropism first relies on the specific interaction between the virus surface protein and a host cell receptor to enter a target cell. Once they’ve entered a host, viruses have to evade the host’s natural, in-built defence system (the immune system) to make additional copies of virus genomes and viral proteins to generate progeny virus particles to initiate another replication cycle. Propagation occurs only when viruses can overcome all of these hurdles.

In general, most viruses are species specific.

Virus spill-over events happen when a particular virus is able to overcome its host’s natural barriers of defence, often through mutations (changing one genetic code at a time) or recombination (replacing a large segment of genetic codes with related viruses), giving it the ability to propagate in a new target species that was not its natural host.

Whenever there is a spill-over event into a new host, it is normal that the defence system in the new host would not know how to handle this new virus, resulting in infection.

Although viruses try to cross their host’s barriers all the time, mostly we would not be aware of this as they are naturally fought off by our defence (immune) system.

What are some well-known diseases caused by coronaviruses that infect humans?

Out of the hundreds of coronaviruses circulating among animal species, there are only seven coronaviruses currently known to infect humans. Three of the seven can cause severe symptoms while the other four only elicit mild symptoms.

The three severe disease-causing coronaviruses are zoonosis events that originated from bats, and they are:

1. Severe Acute Respiratory Syndrome Coronavirus [SARS-CoV]
2. Middle East Respiratory Syndrome – Related Coronavirus (MERS-CoV)
3. Severe Acute Respiratory Syndrome Coronavirus 2 [SARS-CoV-2]

The four coronaviruses that elicit mild symptoms are:

1. human coronavirus OC43
2. human coronavirus HKU1
3. human coronavirus 229E
4. human coronavirus NL63

These four mild coronaviruses are more readily detected in humans during the winter months when humans are more likely to gather indoors.

COVID-19 and SARS-CoV-2

COVID-19 stands for COronaVIruses Disease 2019. On 11 February 2020 the World Health Organization announced the official name for the disease that started the 2019 novel coronavirus outbreak, first identified in Wuhan China.

SARS-CoV-2 is the virus that causes COVID-19.  In other words, SARS-CoV-2 is the infectious agent or pathogen that causes the disease COVID-19.

An analogy would be HIV is the virus (infectious agent) that cause AIDS (the disease) in humans.

What’s the difference between SARS-CoV and SARS-CoV-2?

SARS-CoV and SARS-CoV-2 are two highly related viruses. The natural host of SARS-CoV is a bat, while the natural host of SARS-CoV-2 is not absolutely known, but is likely to also be a bat.

Some major differences between SARS-CoV and SARS-CoV-2 are:

1. the higher hospitalisation-rate (HR) and intensive care-rate (IR) in SARS-CoV (HR-70%; IR-40%) than SARS-CoV-2 (HR-20%; IR-0.06%)
2. the shorter incubation period for SARS-CoV (2-7 days) than for SARS-CoV-2 (4-12 days)
3. the longer interval between symptoms onset and maximum infectivity for SARS-CoV (5-7days) than for SARS-CoV-2 (0 days)
4. the lower portion with mild illness for SARS-CoV than for SARS-CoV-2

All in all, there are more people moving around in the community not knowing their infection status and transmitting SARS-CoV-2 to others, therefore rapidly amplifying the pool of infected people.

For further information, view this research paper: Comparing SARS-CoV-2 with SARS-CoV and influenza pandemics

How is SARS-CoV-2 transmitted in humans to cause infection?

Similar to influenza and the common cold, SARS-CoV-2 is transmitted through close contact. Early research suggested that SARS-CoV-2 was transmitted via droplets. More recent research suggests that SARS-CoV-2 can be transmitted through much finer droplets/particles, enabling the virus to move in air for longer before falling onto the ground. Consequently, this results in a greater transmission rate.

How is the Institute for Glycomics tackling COVID-19?

Four teams of expert scientists from the Institute for Glycomics are using a multi-pronged approach to target the virus SARS-CoV-2 to discover new vaccines and drugs to prevent or cure COVID-19.

• Team 1 is using advanced ex vivo (outside the body) human respiratory system models to evaluate existing drugs, and combinations, as drug candidates to prevent or treat COVID-19.
• Team 2 is working closely with the other research teams within the Institute for Glycomics, as well as with colleagues at the Gold Coast University Hospital and overseas collaborators to develop a vaccine for COVID-19.
• Team 3 has developed propriety biophysical drug screening approaches that allow for the rapid screening of known drugs that can be repurposed to target crucial steps in infectious disease processes. These approaches, in combination with computational biology approaches, are being applied to find solutions to COVID-19.
• Team 4 is working to establish a rapid assay system to evaluate potential drug and vaccine candidates that can prevent the entry of SARS-CoV-2. This system is currently being used in collaboration with other research teams within the Institute for Glycomics for the development of therapeutics.

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