You have all heard about coronavirus – but what exactly is it?
The new coronavirus is named SARS-CoV-2 which causes the disease called COVID-19.
Coronaviruses are a large family of viruses. They get their name from the crown-like spikes that can be seen on their surface with electron microscopy.
Figure 1. 3D medical animation showing the structure of a coronavirus.
This group of viruses were first identified in the 1960s and they can cause a spectrum of disease, from very mild symptoms (like a common cold), to severe disease in some cases.
Making the Jump
There are many coronaviruses that can infect animals and some that can infect humans. Rarely, one of the viruses infecting animals may evolve to infect humans and spread between them. A disease that can be passed from animals to humans is called a zoonotic disease. This is what has happened in the current outbreak- the virus which previously existed just in animals was transmitted to a human, becoming a zoonosis.
There are other examples of coronaviruses evolving to infect humans. For example, you may have heard of Severe Acute Respiratory Syndrome, or SARS, which emerged in 2002 and is thought to have come from civet cats, or Middle Eastern Respiratory Syndrome, MERS, which emerged in 2012 from dromedary camels.
Figure 2. Dromedary camels, a host of MERS virus.
Live markets (where animals are sold whilst still alive) are often linked to zoonotic disease outbreaks. This is because there are lots of interactions between animals and humans. This increases the chances that a virus affecting
an animal will be passed on to a person, thus causing a new zoonotic disease.
How does a virus jump from infecting animals to infecting humans?
Viruses use receptors on their surface to invade animal cells. These receptors can evolve to allow the virus to invade human cells instead. If an animal with this new virus comes into contact with a
human the virus can make the ‘jump’. We think this is how this new coronavirus came to infect humans.
Where did COVID-19 Come from?
The new type of coronavirus causes COVID-19 and cases were first reported in December 2019 in Wuhan, a city with a population of around 11 million and the capital of Hubei Province, China (Map). It is also not yet clear which animal the new coronavirus
lived in previously, although there have been data suggesting this virus it is similar to those found in some bats.
Map showing Wuhan province in China.
Because COVID-19 is a novel disease, no one has ever experienced the disease before. This means that everyone is vulnerable to disease, and you have no protection against it. This is a common problem with zoonotic diseases. Because they come from
animals, humans have no previous experience of infections and thus no protection. It is therefore important to develop vaccines against this new coronavirus, so that we can protect vulnerable people (the sick and the elderly) before they become infected.
Cells: the basic building blocks of all animals and plants. You need a microscope to see most human cells.
Pathogen: Microorganism that causes disease.
Receptors: specialised structures on a cell’s surface that allow communication between the cell and the extracellular space. These can also link with and be recognised by a virus as a gateway for cell entry.
Respiratory: Of or involving the respiratory system (nasal cavity, trachea, lungs etc.).
Vaccine: Substances containing disabled tags of a particular pathogen, usually given via injection. Vaccines stimulate the body to produce antibodies to provide immunity against that pathogen.
Virus: An ultramicroscopic infectious non-cellular organism that can replicate inside the cells of living hosts, often with negative consequences.
Zoonotic disease: A disease which can be transmitted from animals to humans. Rabies is a zoonotic disease. SARS-CoV-2 became a zoonotic disease when a human caught it from an animal host.
To find out more, look at:
1. The World Health Organisation's coronavirus page.
2. BBC Bitesize's guide to coronavirus.
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Figure 1. 3D
medical animation still shot showing the structure of a coronavirus. Accessed
Figure 2. Dromedary camels Credit N. Lathee via https://horizon.lshtm.ac.uk/portal/webclient/index.html#/desktop
Figure 3. Map
showing location of Wuhan, China Source Petrexgmbh accessed via: https://www.petrexgmbh.com/hubei-province/