Ever wondered how COVID-19 affects the body?

The acknowledgement of viruses was unheard of until around the end of the 19th century. The first understanding was the discovery of vaccines heavily influenced by Edward Jenner and Louis Pasteur, however, even though these two remarkable scientists influenced discovery in this area they were unaware that viruses even existed. In1892, Dimitri Ivanosky initiated research with sap extracted from a diseased tobacco plant, filtered and then observed that other plants progressed into a diseased state even after the sap had been filtered, later the infectious substance had been referred to as a 'virus', virus meaning "a substance produced in the body as a result of a disease, especially one capable of infecting others".


Viral pandemics are nothing new though, although at the time they were not understood recorded history has shown evidence of many pandemics dating longer than over 3000 years ago. Although a pandemic is referred to as a disease prevalent to a country or the whole world, meaning that they mostly are either led by bacterial or viral infections. however, other scenarios may cause disease like prions which induce misfolding protein, leaving the proteins essentially unusable. As protein become disrupted by prion proteins, they themselves act as a prion protein disrupting other proteins. An example of prion disease is Creutzfeldt-Jakob disease (CJD), also known as mad cow disease, which is a rare rapid neurodegenerative disease that leads to the onset of dementia and ultimately death. 

Covid-19 was something to be expected which has been on the radar for scientist for many years. This is because Covid -19 is related to the SARs family, by which previous threats have been made from other SARs strains that could have potentially gone viral. The last SARs threat occurred in 2002-03, whereby 8000 people were infected and 800 had died. However, SARs are not the only viral strains to cause a pandemic threat, remember Ebola, influenza, Zika, Nipah. There are still many threats that could lead to a pandemic; each of these viruses is family names meaning that there could be hundreds if not thousands. For example, SARS-CoV-2 (COVID-19) is genetically related to the SARs (Severe acute respiratory syndrome) coronavirus outbreak in 2002-03.

How does Covid-19 affect the body?

Just like most viruses, COVID-19 targets healthy cells to infect overtaking the cells machinery to replicate copies of itself. Essentially, viruses are made of a protein coat also know and a viral capsid, transporting either stands of DNA or RNA. The DNA (Deoxyribonucleic acid) and RNA (Ribonucleic acid) are instructions to make the virus. The outside of the protein coat contains many spikes some of which have evolved to mimic a specific shape to bind to certain cellular receptors on their target host. If a virus can not bind to these receptors then the virus will not gain cellular entry. This is where you will see virus pandemics related to specific species, however, in some cases like COVID-19 slight mutations in these spikes can allow for transition from one animal to another. Surrounding the virus is a membrane envelope collected upon exocytosis (as the virus leaves the cell). Specifically, COVID-19 has spikes that bind to the transmembrane protein Angiotensin-converting enzyme-2 (ACE2) that is slightly embedded into the cells surface. ACE enzymes tend to be regulated by ACE2 after many processes lead to vasoconstriction plus many other roles. ACE2 is found in many respiratory cells and other cells throughout the body. 

COVID-19 will bind to ACE2 with the evolved to fit spike protein. It is essentially the same as copying someone else's key for their house so you can gain entry and walk-in whenever you like. The virus will then undergo endocytosis to gain entry into the cell. Once inside the cell will begin to break down the protein coat with enzymes such as lysosomes. As COVID-19 is an RNA virus it will act as a messenger, meaning that the RNA will bind to the copying machinery (ribosomes) to produce the protein structure reading from the instructions presented by the RNA. Essentially the ribosome will read the RNA strands which instructs what sequence to place the amino acids, once complete a virus would have been produced. This process occurs thousands of times in one cell, all being released as the cell burst into the body to infect other cells. As the cell bursts, the cell will release signalling proteins called interferons which alert nearby cells to heighten their anti-viral defence whilst also stimulating immune cells to the location. However, some studies have shown that COVID-19 has mutated to lower the production of interferons from the host cell allowing the virus to go undetected for a little longer. 

The bodies immune response to COVID-19

The body contains the organs of the immune system which protects the body from internal and external threats such as harmful substances, germs and cellular changes. An important feature of the immune system is the white blood cells (leukocytes) whose role is to travel throughout the body to detect and foreign bodies like bacteria or viruses. To strengthen this there is great communication between the lymphatic system and stresses found in the circulatory system via the exchange of cells and fluids between the two systems. There are three types of immune responses innate immunity (rapid response), adaptive immunity (slow response) and passive immunity. Skin and inflammatory responses are initiated when the body is infected this increases blood flow and allows the immune system to relay information between the bloodstream and lymphatic system. Initially, the immune system will struggle to fight the virus. Over time, the adapted immune response has use B-cells and T-cells. T-cells stimulate B-cells to begin to make y-shaped proteins known as antibodies, whilst also producing cytokines, messenger proteins to alert the immune system to increase its response and to stimulate infected cells to undergo apoptosis (cell suicide). 

Usually, those who have a healthy immune system would eradicate the infection within a couple of weeks, mostly due to the slow but effective response of the adaptive immunity. However, those who have a deprived immune response due to illness or a slower response due to age may struggle to eradicate the infection without a vaccine or medical intervention. Essential the virus replicates faster than the immune response leaving most of the fight to the innate immunity. The innate immune response will increase blood supply and inflammation. Over time these areas become full of dead white blood cells, viral proteins and cellular debris creating a lot of fluid, not a good scenario for the lungs relying on gaseous transfer. In response, the body will undergo acute respiratory distress caused by the increased fluid and hyper inflammation of lung tissue. The by-product of the battle for some cases has been found to lead to sepsis due to the overactive immune response throughout the body as the virus has spread, whereas in most cases people who struggle to overcome the infection will suffer from pneumonia of both lungs.

As you can see COVID-19 has a massive impact on our bodies and needs to be taken seriously. Learning from this pandemic is vital for the future as there will be many more viral pandemics with our growing population. Viruses are constantly mutating due to replication machinery producing many different strains that could pose more threatening viruses. 

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Future articles include:

  • How do covid Vaccines work?
  • Will the Covid 19 pandemic ever end?
  • Will Covid 19 mutate and become more deadly?

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