At the moment there is plenty of information as to what exactly the novel human Coronavirus COVID-19 does to the body. We’ve learnt so much in the time that has passed since the first confirmed infections, but still don’t know enough about all that the virus can do once it infects a person. As the months pass we’re seeing new symptoms being associated with the novel Coronavirus infection, some of which are almost hard to believe. For instance, the latest new symptom of COVID-19, dubbed “COVID toes”, indicates an underlying limb ischemia or, in layman’s terms, restriction of blood and subsequently also oxygen to limbs. This results in swollen and painful toes with visible red and purple spots indicative of tissue damage as a result of oxygen deprivation.
Is red and purple, swollen toes a symptom we’d normally consider for a viral infection, which COVID-19 is? Of course not. But nonetheless here we are. The emergence of new COVID-19 symptoms such as swollen red toes, fingers or bluish lips is definitely a source of stress and anxiety, and also disbelief, and is currently straining the relationship between the people and authorities even more than the pandemic itself. However, it is not proof of incompetence as some suggest, nor a reason to not believe in COVID-19, but a sign of our growing understanding of the novel human Coronavirus and what it does to the body. So as seemingly unrelated to a viral infection as they may appear, any and all new COVID-19 symptoms are just us noticing more of the virus’ effects and represent vital clues to discovering how it works. With this in mind, here is what COVID-19 does to the body, from our current knowledge of its modus operandi:
Effects of COVID-19 on the upper respiratory system
The upper respiratory tract is the entryway of the novel Coronavirus and the starting point of the infection. The throat and nose in particular favor infection seen as they are both the most likely entryways and the ones most likely to receive a higher viral load. The virus attaches itself to cells via an enzyme known as angiotensin converting enzyme 2, ACE2 for short. The ACE2 enzyme acts as a receptor for the virus, allowing it to enter cells and produce infection. COVID-19 replicates at the level of the upper respiratory system which triggers the immune system response and the early symptoms of a COVID-19 infection such as a sore throat, fever (low and high-grade), nasal congestion alternating with a runny nose, headaches, a sore throat, coughing and also loss of smell or taste and more. After sufficient replication, the virus can advance to the lower respiratory tract.
Effects of COVID-19 on the lungs
From the upper respiratory tract, COVID-19 advances to the lower respiratory tract consisting of the lung system (lungs, bronchi, bronchioli and alveolar sacs or air sacs containing pulmonary alveoli lined with mucus and covered with tiny blood vessels known as capillaries).
What happens when COVID-19 reaches the lungs? First of all, the virus attaches itself to lung cells, especially to lung type 2 cells in pulmonary alveoli which contain the ACE2 enzyme. The enzyme acts as a receptor for the novel Coronavirus (SARS-CoV-2) which makes the lungs system a perfect medium for virus multiplication. The virus attaches itself to the host lung cell membrane and infiltrates its genetic material (RNA material), taking over the cell and its functions and making it produce copies of itself to serve infection. Symptoms soon ensue and include shortness of breath, fever and coughing, chest pain, pressure or tightness. In severe cases, infiltration of fluids in the alveolar sacs (air sacs), pneumonia, lung tissue damage and respiratory failure are known to occur and lead to mechanical ventilation. Coronavirus-related lung function impairment can persist for months to years following a severe form of the infection. See the full list of COVID-19 symptoms from most to least common.
Effects of COVID-19 on the immune system
Cytokines are small proteins of the immune system. That is, they fulfill immune system-related functions, notably cell signaling for the purpose of ensuring the immune system response. There are several different kinds of immune system cells that make cytokines as part of the immune system response. Cytokines perform a host of actions such as: they trigger inflammation, activate various immune system cells etc. Sometimes, when there is a more serious infection or disease in the body, the immune system (overreacts and) releases too many cytokines causing what is known as a ‘cytokine storm’ or ‘cytokine release syndrome’. This is an overreaction of the immune system and can create a cascade of events that worsens one’s health to the point of fatality. Infection with the novel Coronavirus SARS-CoV-2 can cause such an extensive and excessive immune system reaction in some people.
COVID-19 and cytokine storms
Infected cells, such as cells infected with the novel Coronavirus SARS-CoV-2, send off a distress signal which tells the immune system of the infection. The immune system activates and, in response to the infection, immune system cells known as white blood cells produce inflammatory cytokines. The cytokines further activate immune system cells which also react by producing inflammatory cytokines. As you can tell by now, this is an overreaction stemming from an otherwise normal inflammatory immune system response. But the excessive inflammation is damaging to tissues and organs and, if not regulated, ultimately leads to lung tissue damage, heart muscle damage etc. respiratory failure and multiple organ failure. This is because of immune system cells which infiltrate the lungs and heart muscle, and other organs, producing excessive inflammation and subsequent damage.
Effects of COVID-19 on blood vessels and the heart
There is an explanation for COVID toes as they’re called (and not just them), and it’s a good one. The inside of the heart and all blood vessels (arteries, veins and capillaries) is lined with endothelial cells. Endothelial cells have the angiotensin converting enzyme 2, or ACE2. This enzyme acts as a receptor for SARS-CoV-2, making it possible for the virus to attach itself to and infect cells. When the virus infiltrates cells via the ACE2 enzyme receptor, the infected cells send out a distress signal to the immune system. In response, the immune system sends out immune system cells that produce inflammation via inflammatory cytokines to fight the infection. In some cases, the immune system response results in too much inflammation that it destroys tissue, causing tissue damage, including the now famous COVID-19 toes (which is really a form of limb ischemia), but also acute cardiac injury and even heart attacks. The hyper-inflammatory response can disrupt normal clotting mechanisms and further lead to blood clots and associated cardiovascular events.
Effects of COVID-19 on the digestive system
The now famous ACE2 enzyme that acts as a receptor for the novel Coronavirus SARS-CoV-2 is also present on the surface of cells that line the small and large intestine. As SARS-CoV-2 reaches the digestive system and infiltrates cells with the ACE2 receptor, the immune system response is activated and the normal functioning of the cells is disrupted further, resulting in symptoms such as diarrhea, but also nausea, vomiting, loss of appetite or abdominal pain.
Effects of COVID-19 on kidneys
Kidney damage is a serious complication of the novel Coronavirus infection, one that can leave a person with permanent kidney damage, if not worse. The explanation behind the severe effects of SARS-CoV-2 on the kidneys has to do with the kidneys being a potential hotspot for infection. The kidneys can be targeted by SARS-CoV-2 because of the presence of ACE2 receptors on the cells surface. In addition to the tissue damage produced by the virus itself, the inflammation brought on by the immune system response causes further damage. In those that develop more serious forms of COVID-19, the damage can build up and lead to acute kidney injury and kidney failure, with the need for dialysis.
Effects of COVID-19 on the liver
In addition to pneumonia, kidney damage and blood clotting events, the novel Coronavirus has been observed to also affect the liver, causing complications such as acute liver failure, likely due to liver tissue injury. The reason behind why SARS-CoV-2 causes liver failure has not been identified yet, but several causes are possible, including:
- Systemic inflammation in severe forms of the disease which leads to multiple organ damage, including liver damage;
- Disruption of normal clotting mechanisms which impacts liver function;
- Kidney failure, also observed in severe forms of COVID-19;
- Adverse reactions to various therapies, including the use of paracetamol for fever treatment;
- Existing pathologies or liver conditions that can no longer be managed.
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