In some, the coronavirus causes only a mild fever, while others cannot breathe and die. Why? The Danish Videnskab explains what happens in the patient's body and when there are severe respiratory complications when even artificial ventilation does not help.
While some have very mild symptoms of coronavirus, others may die from it.
“The coronavirus does not often penetrate so deep into the lungs, but if it does happen, you are in great danger. Even if a patient is connected to a ventilator and 100% of the required oxygen is pumped into the respiratory system, in the most severe forms of ARDS (that is, acute respiratory syndrome), it is impossible to maintain a normal blood level,”says Christian Wejse. Lecturer at the Institute of Public Health at Aarhus University and expert in infectious diseases.
What happens when small particles of the virus enter the body, and how do they manage to cause such harm that the patient becomes ill even with supplemental oxygen?
In this article, we'll dive deeper into cells to learn more about how a virus called SARS-CoV-2 develops step by step.
The virus makes body cells work for themselves
We have already talked about how exactly you can get infected with coronavirus, so we will skip this stage here.
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Droplets of liquid with virus particles enter your body through your eyes, nose or mouth - and now you are already infected. The virus particles immediately enter the so-called epithelial cells in the respiratory tract. There they begin to command their new host cells, ordering them to make multiple copies of the virus.
The purpose of these copies is simple. They must invade as many cells in the airways as possible before the immune system detects that something is wrong.
The most important task of immunity is precisely to prevent the virus particles from reaching the cells that are deep in the lungs, because it is there that the virus can do great harm.
Having found an uninvited guest, the immune system beats the alarm and forces the affected cells to produce the signaling substance interferon. This protein "programs" special protective cells to destroy their fellows infected with the virus. Thus, interferon prevents the virus from filling all the lungs.
This is why headache, fever and cough begin
If the immune system manages to defeat the particles of the coronavirus while they are in the upper respiratory tract, the sick person will get off with mild symptoms: fever, dry cough and headache.
The cough begins already when the virus enters the cells of the upper respiratory tract and irritation begins, scientists say.
Some patients with coronavirus also suffer from cold symptoms, if particles of the virus are inhaled through the nose, and they remain on the mucous membranes. Others cough up phlegm, which leaves infected cells that have been killed by the immune system, says Christian Weisse.
"A fever starts when the immune system triggers the production of interferon, because this process raises the body temperature," he explains. "When the temperature rises, the blood flow to the brain increases, and therefore the head hurts."
This stage usually lasts four to six days, and medical attention is usually not required. However, the patient should stay at home, have as little physical contact with the family and pay more attention to hygiene, the health department recommends.
When interferon, on the orders of the immune system, kills all the affected cells, the temperature will drop and the person will recover. This will stop the disease in most infected people, studies show.
When the disease gets serious
But for some people with COVID-19, symptoms go beyond fever, cough, and headache.
When a coronavirus infection seriously infects the body, acute respiratory syndrome can develop, says Christian Weisse.
"This is a very, very severe pneumonia, in which so much fluid accumulates in the tissues of the lungs that oxygen simply cannot enter the bloodstream," he explains.
The prerequisites for acute respiratory syndrome are associated with the fact that the immune system either fights the virus very poorly, or did not detect it in the body at all.
In this case, the particles of the virus spread freely through the cells and eventually get to the alveoli. These are tiny sacs located at the ends of the ducts that run through the lungs. The air we breathe with oxygen gets there.
The alveoli perform an important function, because it is thanks to them that oxygen is sent through the small blood vessels to all the cells of the body so that they can do their job. The cells of the body, in turn, through the vessels send back to the alveoli unnecessary waste matter - carbon dioxide. This exchange is called diffusion.
Immunity detects danger too late
If the virus particles have already managed to reach the alveoli, when the immune system finally begins to fight them, the exchange of oxygen (primarily) and carbon dioxide (to a lesser extent) may be disrupted.
When interferons and other signaling substances activate the soldiers of the immune system - leukocytes - and they begin to destroy cells infected by the virus, the body tries to repair damage by creating scar tissue - for example, in the alveolar walls, through which oxygen enters the blood vessels.
And although the "intentions" of the body are good, the scar tissue does not let oxygen into the blood vessels, and does not allow carbon dioxide to leave them, therefore it takes more time to exchange oxygen and carbon dioxide.
“The longer these processes take place in the lungs, the harder it is for a person to breathe. He begins to breathe in air faster and more often, because the blood is poorly saturated with oxygen, and as a result, oxygen ceases to enter the body at all,”explains Christian Weisse.
Fluid in the lungs interferes with breathing
At the same time, the virus can provoke irritation and inflammation of the lung tissue.
The blood vessels around the alveoli are so thin that holes appear in them and fluid from the inflammation begins to seep into the alveoli. This makes breathing even more difficult, and the patient is connected to a ventilator.
When the cells of the body stop receiving oxygen, inflammation spreads throughout the body, and the immune system is no longer able to fight the virus, the person dies.
However, despite the fact that COVID-19 can cause extremely serious complications, the estimated death rate from it is relatively low compared to, for example, SARS, from which 10% of all cases died.
By comparison, the death rate from coronavirus in Denmark is expected to be between 0.3 and 1%, according to estimates by the health department.
Anne Sophie Thingsted