Infection, replication, destruction. What actually is coronavirus and what does it do?
You’ve all heard its name, you all know what’s happening across the world right now, and we are all acutely aware of the danger. So, I’ll spare us all and won’t retread that old ground.
It seems like every day this deadly new virus gains a foothold in a new country and spreads quickly. It’s scary. It scares me. If it scares you too then I truly empathise. But when something scares me I find the more I learn about it, the less it scares me.
What really rattles people isn’t the word “virus”, we’re used to them, it’s the word “new”. We fear what we don’t know and what we don’t understand. And, if you’re like me, the wishy-washy explanations of the coronavirus you find in mainstream news articles just do not soothe my frayed nerves enough.
So, I went into full research mode and this is what I found.
Firstly, it has nothing to do with beer, let’s just get that out of the way with, although they do share the same origin: Latin. Corona is the Latin for ‘crown’, hence the beer’s logo being a crown. It’s also where The Sun’s corona received its name (technically from the original Ancient Greek ‘ κορώνη’, which the Latin is a derivation of), the aura (or crown) of plasma which surrounds our native star. And this is also where the ‘corona’ in the coronavirus derives its name, as the club-like protrusions (peplomers) on the virus’ main body (capsid) give an appearance somewhat similar to The Sun’s corona when viewed through electron microscopy.
The name ‘coronavirus’ isn’t actually specific to any one virus, but all viruses from the Coronavirinae virus subfamily, from the Coronaviridae virus family. This subfamily also contains the infamous SARS-CoV (Severe Acute Respiratory Syndrome Coronavirus) and MERS-CoV (Middle East Respiratory Syndrome Coronavirus) viruses, as well as our perennial tormentor, the common cold (which in itself comprises of over 200 known viral strains).
The particular coronavirus causing havoc at the moment is Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). It is genetically related to SARS-CoV, which caused a global epidemic in 2002–2003. SARS-CoV-2 results in COVID-19 (no please, give it a more terrifying and James-Bond-villain-weapon-like name), which actually translates to COronaVIrus Disease-2019.
COVID-19 can present symptoms such as fever, cough, and shortness of breath. These symptoms can range from minimally symptomatic to acute and life-threatening. This is something we are all intensely aware of currently but how does SARS-CoV-2 actually infect us, makes us sick, and spread?
How SARS-CoV-2 Works
SARS-CoV-2 acts like most other coronaviruses, in the sense that it invades our cells and uses our own cellular machinery to replicate itself. It essentially uses our cells as virus factories.
OK, let’s take a step back and briefly discuss some of our usual cellular machinery. Much of what human cells are made up of are proteins. We create these proteins ourselves within our cells, using genetic blueprints we call genes. Our genes are basically just long stretches of our DNA.
The DNA which encodes a gene is essentially ‘unzipped’ and transcribed into something called messenger-RNA (mRNA). mRNA is a single-stranded molecule which is similar to DNA (but DNA is double-stranded), created specifically to make a particular protein. This mRNA is then translated into a string of amino acids, which eventually fold up into said protein.
Within the capsid of a SARS-CoV-2 virion (a single virus particle) lies its own genetic material; a single-stranded positive-sense RNA with a 5′-cap and 3′-poly-A tail. Now, that’s a bit technical even for me, but in basic terms the SARS-CoV-2 RNA works in the same way as our own mRNA. Therefore, the viral RNA hijacks our own cellular machinery to replicate all the materials it needs to build new virions. These virions then exit our cells and move on to infect other cells and replicate more of the virus. And the cycle continues.
How SARS-CoV-2 Affects Us
OK, so we know how the virus replicates and spreads, but why, and how, does it make us so sick?
When a virus monopolises our cellular processes to replicate itself, it often disrupts the host cell’s homeostasis (the maintenance of an optimum environment) and causes irreparable damage to the cell, resulting in cell death.
In the case of SARS-CoV-2, the virus initially targets two types of lung cells: cells that produce mucus and ciliated cells, which use their cilia (hair-like structures that line the cell) to filter debris and pathogens with the mucus and move them up the respiratory tract so they can be swallowed and destroyed in the stomach. Just like SARS-CoV, SARS-CoV-2 kills these ciliated cells, which then allows debris and fluids to fill your airways and block your alveoli, the air sacs in your lungs where oxygen enters the blood, causing shortness of breath. In severe cases, this can lead to pneumonia and possible morbidity.
Until a vaccine is ready to be distributed, our immune system will do much of the work in fighting a SARS-CoV-2 infection. However, this can be a double-edged sword.
The Immune Response
Our bodies are attuned to recognising foreign substances, including viral infections of cells. A group of proteins, called cytokines, are released in areas of infection and ‘tag’ infected cells for destruction by our immune system, in an effort to stop the replication and spread of an infection. This is how the immune system also responds to coronaviruses, including SARS-CoV-2. And, for the most part, this response aids in the ultimate destruction of the virus. Early data, so far, suggests that around 82 per cent of cases present with milder symptoms.
However, sometimes our immune system overreacts, known as a hyperactive response. Usually, our immune system response is tightly regulated and targets only infected areas but in the event of a hyperactive immune response, our immune system struggles to differentiate between infected and healthy cells, and begins to destroy all cells in its path. This ultimately leads to more damage, rather than less. It is believed that hyperactive immune responses are worsening the effects of the infection in some patients, and increasing chances of severe pneumonia by increasing cellular debris and fluids in the lungs.
Immune system hyperactivity was also recorded in SARS-CoV patients, and it is believed that this hyperactivity was the cause of permanent damage to the lungs in the form of lesions and scar tissue. This damage is also being recorded in SARS-CoV-2 patients.
After days upon days of research, am I worried? Well, yes. No one wants to get sick. Am I scared? No. SARS-CoV-2 is an awful virus but it is no longer a mystery to me, and it’s that mystery that causes us so much anxiety.
At the moment, the WHO put the global death rate at 3.4 per cent, but there is speculation that this could come down and, in some countries, become more in line with severe seasonal flu. In the U.K., the death rate is at around 0.73 per cent, with 273 confirmed cases and 2 confirmed deaths (at the time of writing this article).
So what should we do? You are likely asking asking, and the answer is simple: don’t panic. Remain calm and listen to the advice of your government and health officials.
Chen, N., Zhou, M., Dong, X., Qu, J., Gong, F., Han, Y., Qiu, Y., Wang, J., Liu, Y., Wei, Y., Xia, J., Yu, T., Zhang, X. and Zhang, L. (2020). Epidemiological and clinical characteristics of 99 cases of 2019 novel coronavirus pneumonia in Wuhan, China: a descriptive study. The Lancet, 395(10223), 507–513.
Chen, Y., Liu, Q. and Guo, D. (2020). Emerging coronaviruses: Genome structure, replication, and pathogenesis. Journal of Medical Virology, 92(4), 418–423.
Li, G., Fan, Y., Lai, Y., Han, T., Li, Z., Zhou, P., Pan, P., Wang, W., Hu, D., Liu, X., Zhang, Q. and Wu, J. (2020). Coronavirus infections and immune responses. Journal of Medical Virology. 92(4), 424– 432.
National Geographic. (2020). Here’s what coronavirus does to the body. [online] Available at: https://www.nationalgeographic.co.uk/science-and-technology/2020/02/heres-what-coronavirus-does-body.
Zou, L., Ruan, F., Huang, M., Liang, L., Huang, H., Hong, Z., Yu, J., Kang, M., Song, Y., Xia, J., Guo, Q., Song, T., He, J., Yen, H., Peiris, M. and Wu, J. (2020). SARS-CoV-2 Viral Load in Upper Respiratory Specimens of Infected Patients. New England Journal of Medicine.