Coronavirus

There are many different viruses. Coronaviruses are a group of viruses that cause diseases in birds and mammals. They are all similar in their shape, and in humans, they often cause upper respiratory illnesses.

Rights: scientificanimations.com, CC BY-SA 4.0

Coronavirus structure

Coronaviruses all contain RNA surrounded by a lipoprotein coat. In 2020, this SARS-CoV-2 virus caused the COVID-19 pandemic.

(Labels have been adapted from the original by scientificanimations.com).

Transmission of coronaviruses

Coronaviruses are zoonoses, which means they can be transmitted between animals and people. This means that they can jump the species barrier. These recent outbreaks of coronavirus have been particularly dangerous for humans:

• SARS-CoV, which transmitted from civet cats to humans in 2003, causing Severe Acute Respiratory Syndrome and killing 774 people worldwide.
• MERS-CoV, transmitted from dromedary camels to humans in 2012, causing Middle-East Respiratory Syndrome and killing 858 people worldwide.
• the newest coronavirus transferred from animals to humans in 2019. The virus has been named SARS-CoV-2, and the disease it causes is called COVID-19 (Coronavirus Disease-2019).

When a coronavirus infects a human host, human to human transmission is rapid. The virus spreads easily in small droplets, especially when someone who is infected coughs or sneezes. These small droplets of saliva or mucus containing the virus land on surfaces and can remain intact for some time – ready to infect another human host. This is why we can slow down the spread of viruses by covering our mouths and noses when we sneeze or cough, washing our hands thoroughly and regularly with soap and cleaning surfaces regularly.

Rights: Public domain

Sneezing and coughing

We often don’t think of how much saliva or mucus we expel when we cough or sneeze. This image shows the potential of the spread of microbes like viruses when we do not cover our mouth and nose when we cough or sneeze.

How viruses replicate

Viruses consist of RNA surrounded by a lipoprotein coat. On their own, they can’t grow, move, eat or breathe. So how do they continue to multiply and cause such harm?

Viruses insert their genetic material into host cells, hijacking the host cell’s protein synthesis process to produce so many copies of the virus that they burst the membrane of the host cell, killing it. This causes pain. It also releases millions of viruses into the host to then infect other cells.

Because trillions of copies are made of the viral genetic material over time, mutations can occur. These cause different strains of the same virus.

How our bodies respond

Our bodies have an effective immune system that identifies anything ‘foreign’ – substances, like viruses, that aren’t supposed to be there. For new infections, it can take our body time for our immune system to destroy the virus. Our immune system needs to first identify antigens of the virus. This triggers the production of antibodies that will tag the virus for destruction. If you have been exposed to the same virus before – for example, chicken pox – your body will recognise the virus quickly and often destroy the virus before you have any symptoms.

The common symptoms of COVID-19 are respiratory symptoms, fever, cough, shortness of breath and breathing difficulties. Our immune system will work to eliminate this new virus from our bodies, but in severe cases, a person’s immune system cannot respond quickly enough. This is why the elderly, those with underlying health issues and people who are immunocompromised are more at risk.