COVID-19 Causes

Covid-19 has been the talk of people around the world since 2019. News, articles, families and friends could not stop mentioning it. So, what is this Covid-19? What kind of illness is it, and what are the causes? 

What is COVID-19?

Covid-19 (Coronavirus disease 2019) is an illness caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).1 It is highly infectious and deadly , compelling the World Health Organization (WHO), to declare it a global pandemic in March 2020. Since then, Covid-19spread quite rapidly like wildfire, infecting people worldwide, overwhelming many healthcare systems and taking the precious lives of 6 million people as of March 2022.1 Therefore, it is vital to know the symptoms of Covid-19. 

Symptoms of COVID-19

Patients with Covid-19 might elicit various symptoms, ranging from asymptomatic(mild symptoms) to severe illness and death.3 Typical symptoms of Covid-19 include fever, cough and shortness of breath.1,3 Some patients also reported other symptoms such as weakness, malaise, muscle pain, respiratory distress, sore throat, and loss of taste and/or smell. 1 However, patients with asymptomatic Covid-19 or anyone with a high risk of exposure to Covid-19 should get themselves checked even without symptoms.1

The COVID-19 virus

What is a virus?

You probably have heard the word “virus” at least once in your lifetime. But what is a virus? 

Viruses are infectious agents with diameters of about 16 nm to over 300 nm.4 With their small size; they can pass through filters. 4,5 Can you imagine how small a virus can be? Human hair is roughly 80,000-100,000 nm wide. If we compare a 100 nm virus particle to an 80,000 nm human hair, this makes the human hair to be 800 times larger! 

Viruses contain only one kind of nucleic acid, either DNA or RNA. 4,5 They have no ribosomes, mitochondria or other cell-like organelles. 5 Unlike some bacteria or other single-cell microorganisms (protozoa) that can reproduce on their own, viruses need a host cell to replicate.5

Fun fact

 Viruses do not reproduce by division like bacteria, yeasts or other cells.4,5 Their replication occurs as a burst of thousand of virus particles from a single virus in a span of short time.5

How does the COVID-19 virus cause the symptoms?

Viral life cycle and subsequent symptoms of infection: remember to use as plain language as possible

Just imagine the coronavirus like a ball that consists of five proteins, namely spike (S), envelope (E), membrane (M), nucleocapsid (N) and haemagglutinin-esterase (HE).6 

RNA, which is responsible for the replication of the virus, is inside the coronavirus and bound together with N-protein.6 Meanwhile, the S, E, and M proteins are on the surface of the virus.6

The coronavirus can infect two types of lung cells: the goblet and ciliated cells.6 The goblet cells produce mucus that prevents our lungs from drying and protect them from pathogens (microorganism that can cause disease).6 On the other hand, the ciliated cells play a crucial role in clearing debris from the lungs by eliminating mucus.6

The spike protein will bind to the host cell receptors, called ACE2, found in human cells in the lungs, heart, kidney and intestines.6 S-protein binding onto the ACE2 receptors allows the virus to enter the human cells via endocytosis.6 Once inside the cell, the virus releases its RNA and starts to replicate itself. 6

The newly replicated virus will then release out of the infected cells by a process called exocytosis, which will trigger cell death or apoptosis. 6 The accumulation of dead cells will eventually fill the lungs with fluid and debris, causing clogging, which can lead to pneumonia. Sometimes our immune systems act up and damage healthy lung tissues, which might lead to more cells dying. Thus, it will further clog the lungs and worsen pneumonia. Continuation damage to the lung can cause complete respiratory failure, eventually leading to death.6

When should you see a doctor?

Most people with Covid-19 will feel better after a few weeks. You may be able to look after yourself at home until then. However, you might have to see your doctor immediately if you’re showing any of these signs:

  1. Breathless
  2. Constantly feel pain or pressure in the chest
  3. Difficulty in waking or staying awake 
  4. Pale, grey or blue-coloured skin, lips or nail beds (depending on your skin tone)

However, this list does not cover all the possible symptoms out there. If you and the people you know are struggling, please call your general practitioner immediately. 


Summary of everything above

Covid-19 is an illness caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). People with Covid-19 usually have fever, cough and shortness of breath. Unlike other pathogens, the coronavirus needs a host to replicate. It infects the host cells by attaching itself to the host receptors, ACE2, and releases its RNA inside the host cells. The coronavirus will likely attack the lung, which can eventually lead to pneumonia and can be fatal. Usually, you can recover by yourself if you have Covid-19. However, seek medical attention immediately if the symptoms are severe and getting worse.


  1. Cascella M, Rajnik M, Aleem A, Dulebohn SC, Di Napoli R. Features, evaluation, and treatment of coronavirus(COVID-19). In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 [cited 2022 Sep 7]. Available from: 
  2. Li H, Liu SM, Yu XH, Tang SL, Tang CK. Coronavirus disease 2019 (COVID-19): current status and future perspectives. Int J Antimicrob Agents [Internet]. 2020 May [cited 2022 Sep 7];55(5):105951. Available from: 
  3. Esakandari H, Nabi-Afjadi M, Fakkari-Afjadi J, Farahmandian N, Miresmaeili SM, Bahreini E. A comprehensive review of COVID-19 characteristics. Biol Proced Online [Internet]. 2020 Aug 4 [cited 2022 Sep 7];22:19. Available from: 
  4. Modrow S, Falke D, Truyen U, Schätzl H. Viruses: definition, structure, classification. Molecular Virology [Internet]. 2013 Aug 12 [cited 2022 Sep 7];17–30. Available from: 
  5. Taylor MW. What is a virus? Viruses and Man: A History of Interactions [Internet]. 2014 Jul 22 [cited 2022 Sep 7];23–40. Available from: 
  6. V’kovski P, Kratzel A, Steiner S, Stalder H, Thiel V. Coronavirus biology and replication: implications for SARS-CoV-2. Nat Rev Microbiol [Internet]. 2021 Mar [cited 2022 Sep 8];19(3):155–70. Available from: 
  7. Haque SM, Ashwaq O, Sarief A, Azad John Mohamed AK. A comprehensive review about SARS-CoV-2. Future Virology [Internet]. 2020 Sep [cited 2022 Sep 8];15(9):625–48. Available from: 

Sentia Racha Keyulong

Bachelor of Science - BSc, Psychology, The University of Edinburgh, Scotland, Scotland

Sentia is an experienced Research Assistant and Medical Writer. presents all health information in line with our terms and conditions. It is essential to understand that the medical information available on our platform is not intended to substitute the relationship between a patient and their physician or doctor, as well as any medical guidance they offer. Always consult with a healthcare professional before making any decisions based on the information found on our website.
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