The number of COVID-19 cases and deaths continue to increase globally. While some people are mildly affected and recover soon, in some patients the condition can worsen drastically, leading to death even. How does COVID-19 kill? As the novel coronavirus results in many deaths, there is a need to understand how it affects various organs and systems, resulting in death.
How Does COVID-19 Kill?
While the study for a better understanding of the pathogenesis and action of the novel coronavirus continues, some information that throws light on its potentially fatal behavior is here. There are many speculations and possible theories about how does COVID-19 kill or how does it affect the various organs resulting in death.
The novel coronavirus infection spreads from person to person through the respiratory droplets from an infected person. These droplets can land on the hands or other surfaces, spread through the hands of the other person. When the other person touches the nose,mouth, and eyes, the virus finds entry into their system. The COVID-19 virus, SARS-CoV-2 enters through these openings having mucus membranes. The virus mainly lands in the lining of the nose. The cells in these areas are rich in angiotensin-converting enzyme – 2 (ACE-2), which is the receptor cell for the novel coronavirus disease.1 Hence, the virus tends to attack cells and tissues that are rich in these receptors.
Once the virus enters into the body, it begins to multiply. It makes several copies of itself, which start invading the new cells and tissues in the area. Due to this, the virus sheds large amounts of mucus during the initial period of infection and the person may or may not have any symptoms. If symptoms are present, usually, fever, dry cough sore throat, loss of smell, taste, headache, or body aches may be seen.2 In some people, the immune system is activated at this stage to curb the infectious attack.
However, in some, the immune response is not effective and the virus can go further down to enter the lower respiratory system. Through the windpipe, it can go down and enter the lungs, which can turn very dangerous. The tiny air sacs in the lungs, called alveoli are also lined by cells that are rich in ACE2 receptors, which causes the infection to reach the lungs. The immune system works hard to get rid of the invading virus. With more and more inflammatory cells begin released, there is an increase in the fluid and pus cells. This is when the stage of pneumonia develops with symptoms of fever, cough, and shortness of breath. During this process, the otherwise normal functioning of oxygen transfer in the air sacs of lungs gets affected, which explains breathing difficulty.
While some recover with oxygen supply, as required, some may deteriorate further, resulting in acute respiratory distress syndrome (ARDS). The oxygen levels can further drop down and breathing difficulty worsens. Most of these patients need a ventilator due to severe disease and some may die from it.
How Does COVID-19 Kill – Deeper And Multiple Invasion
The novel coronavirus can affect deeper into the lungs, in some people, and can cause severe disease. But in some cases, the COVID-19 virus itself or the body’s immune response to it can create a greater impact by affecting multiple organs. According to some studies, the body’s defense mechanism gets stimulated, which may also set the immune system in overdrive. This often results in heightened responses harming healthy tissues as well. Cytokines are a result of inflammation – otherwise necessary for an immune reaction. But the overactive immune system can cause a cytokine storm, which, means an excess of cytokines to the extent that the body’s immune system works in excess than needed.2 In this, it also invades the healthy tissues and can cause damage to other organs in the body.
However, some other researchers differ in their opinion and consider another mechanism that leads to a severe disease state. Some believe that the use of drugs to suppress the immune system can affect the fighting ability, leading to more growth of the virus. Nevertheless, there is some way in which various organs of the body get affected, resulting in rapid deterioration of the condition. When discussing how does COVID-19 kills, it is important to consider the effects of the virus on the other organs and systems as well.
The novel coronavirus diseasevirus SARS-CoV belongs to the beta coronaviruses group and binds to the zinc peptidase angiotensin-converting enzyme 2 (ACE2). This receptor of the novel virus is present on the endothelial cells of arteries and veins, arterial smooth muscle, respiratory tract epithelium, epithelia of the small intestine, respiratory tract epithelium, and immune cells. This possibly explains the affinity of the virus to these organs and systems. The virus can easily bind with these receptor cells to enter into the host cell.3
Cardiovascular Effects in COVID-19
As the COVID-19 virus binds the ACE2 receptors on the cells surface, it can enter into the cells including the lining on the blood vessels. This can explain the worsening of symptoms in those having cardiovascular problems. Some studies suggest that COVID-19 may predispose the patients to venous and arterial thromboembolism due to excessive inflammation, hypoxia, and immobilization and diffuse intravascular coagulation. The study reports have shown that the incidence of thromboembolic complications in ICU patients with COVID-19 infections was 31%, which was high.4
Elderly patients with underlying diseases are more likely to be infected with the novel coronavirus disease and tend to be severely ill. Co-morbid conditions could include hypertension, diabetes, and coronary heart disease.5 It is believed that patients having coronary artery disease and heart failure are susceptible to cardiac injury and when infected with COVID-19 there are greater chances of severe pneumonia, myocardial ischemia, or cardiac dysfunction. Also, inflammatory responses can lead to ischemia. The inflammation can also result in endothelial dysfunction, increasing the procoagulant activity of the blood, which can lead to the formation of an occlusive thrombus over a ruptured coronary plaque.
However, researchers are still trying to understand the exact mechanism behind the deterioration of cardiac health in COVID-19 patients. The virus can directly attack the lining of the blood vessels and the heart due to ACE2 receptors or the severity of disease increases due to lack of adequate oxygen damages the blood vessels or a cytokine storm, causing an excess immune response.
Intestinal and Hepatorenal Effects in COVID-19
As the novel coronavirus affects the heart and the blood vessels, it can directly or indirectly also cause damage to other vital organs. The involvement of the liver and the kidneys explains how does coronavirus kills. Let us understand how it affects these systems.
The patients with COVID-19 have also shown gastrointestinal symptoms, mostly noted early in the disease course.6 Patient reports and biopsy data of COVID-19 patients makes it clear that the virus can enter and affect the lower gastrointestinal tract.
Apart from this, many patients with severe disease of COVID-19 may be at risk of hepatorenal damage. Upto half of the hospitalized patients with COVID-19 had enzyme levels suggesting liver involvement.2 The liver damage could be linked to immune-related injuries like immune system overdrive or the use of drugs to treat COVID-19. Again, the chances of the virus binding directly to the ACE2 receptors is possible, as the receptor cells are present in the liver.
Kidney damage too is common in severe COVID-19 cases. Again, in this case, the virus can attack the kidneys directly by binding to the receptor cells or kidney failure may result from system events resulting in low blood pressure and related changes.2 Studies have reported that those patients having acute kidney injury (AKI) were five times more likely to experience a severe disease outcome like death than those COVID-19 patients without it.2 The risk of kidney damage could also be related to the use of ventilators and drugs to treat severely ill patients of COVID-19.
Effects of COVID-19 on the Brain And Nervous System
In an attempt to understand how does coronavirus kills, it is important to note the effects of the novel virus on the brain. COVID-19 virus can also affect the brain cells and the nervous system resulting in neurological symptoms. Seizure like symptoms, confusion, loss of consciousness, strokes, loss of smell may be seen. The ACE2 receptors present in the brain may explain the possibility of direct injury to the brain cells due to the virus. Although the exact mechanism is not clear. Studies have also found traces of the novel coronavirus disease in the cerebrospinal fluid of a COVID-19 patient who developed meningitis and encephalitis, thus concluding that the virus does penetrate the nervous system in some way.2 But again, the other theories of cytokine storm can cause brain swelling, and the tendency of blood to form clots can trigger strokes. Doctors are trying to figure out the exact cause and way by which the virus affects the brain.
While studies continue to understand the entry of viruses on various organs and systems, various opinions are presented. These theories are based on the various reports received from the studies conducted. Although more research is required to conclude, this fairly explains how does coronavirus kills.