The article has been automatically translated into English by Google Translate from Russian and has not been edited.

What happens in the body after infection with coronavirus and why not everyone is sick equally



Although the procession of the new coronavirus on the planet has been going on for three months, and the authorities of different countries of the world are taking unprecedented measures to restrain it, there are still quite a few ambiguities about what exactly happens in the body when virus particles get into it, writes

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Nevertheless, quite a lot about how COVID-19, a coronavirus-induced infectious disease, is progressing, has already become clear. The New York Times interviewed researchers and experts in the field of medicine, gathering together information about what is now known on this subject and what remains a “blank spot” for now. The material was approved by Russian infectionist Pavel Alexandrov.

How does coronavirus cause infection?

The virus spreads through droplets flying in the air when coughing or sneezing. Drops containing viral particles can enter the body of people around the virus through the nose, mouth or eyes. Drops also settle on nearby surfaces, touching which, and then touching the face, you can also become infected. If viral particles get into the nose, together with the mucus they quickly overcome the nasal passages in order to be on the mucous membrane of the back surface of the pharynx. There they attach to a specific receptor on the surface of the cells, and infection begins.

The surface of viral particles, like spikes, is seated with protein structures that penetrate cell membranes, deceiving receptors and the immune system. The genetic material of the virus, in essence, acts as an invader, virtually crushing the whole cellular metabolism, as if to say: “Stop doing everything that you usually do. Now your job is to help me multiply, ”explained William Schaffner, Specialist in Infectious Diseases at the Vanderbilt University Medical Center.

How does this process cause breathing problems?

As copies of the virus multiply, they break out of the infected cell and capture neighboring ones. Symptoms most often occur on the back of the larynx - a sore throat and a dry cough. Then the virus begins to gradually and steadily move down to the bronchi. When it reaches the lungs, their mucous membranes are literally flammable. Inflammation can damage the alveoli - bubble structures in which gas exchange occurs between atmospheric air and blood. The alveoli have to work hard to saturate the blood circulating throughout the body with oxygen and remove carbon dioxide from it, which is then expelled from the body with an exhalation.

Viral damage to lung tissue makes them vulnerable to bacteria.

Edema and inflammation develop, oxygen becomes more difficult to penetrate through the mucous membrane into the blood, alveoli are filled with fluid, pus and dead cells. Virus-bacterial pneumonia (pneumonia) is rapidly progressing.

This can be followed by the most serious, fatal complication - acute respiratory distress syndrome, in which the lungs generally cease to saturate the blood with oxygen, a large amount of fluid accumulates in them, and the patient must be connected to an artificial lung ventilation device. The reason for this development of events is the so-called “cytokine storm” - due to the hyperactivity of the immune system, which is trying to suppress the focus of inflammation in the lungs, there is a powerful, uncontrolled release of certain proteins, cytokines, which activate the immune cells in the focus. The latter, in turn, throw out a new portion of cytokines, and so on. As a result, a vicious circle forms, which leads to the destruction of not only damaged lung tissue, but also neighboring healthy tissues.

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At the same time, as the professor of pathology from the School of Medicine of the University of Chicago Shu-Yuan Xiao established (Shu-Yuan Xiao), spreading in the lungs, the coronavirus chooses a rather non-standard path. Professor Xiao analyzed the autopsy reports of patients who died from COVID-19 in China and found that the viral invasion begins on the periphery of both lungs, and it takes some time before it reaches the central regions. According to Xiao, this circumstance may explain the fact that at first in Wuhan, where the outbreak of the coronavirus began, and later developed into a pandemic, a lot of cases of the disease could not be diagnosed right away. Therefore, many people with symptoms were sent back home without any treatment, suggesting that they were sick with something else. These people either tried to seek help in other hospitals, or sat at home and infected members of their family and other people with whom they contacted, which was one of the reasons for the widespread infection, the professor said.

This version is indirectly confirmed by the results of a recent study conducted by a team of scientists from the Ikana School of Medicine Mount Sinai Medical Center.

They found that more than half of the 121 patients in Chinese hospitals had absolutely normal lung computed tomography (CT) results at the beginning of the disease. However, as the disease progresses, CT scans begin to show blackouts in the central lungs.

These opaque areas in the foci of inflammation create a characteristic picture of "cobblestone pavement" on the tomogram, reminiscent of different-sized pieces of pavers in the pavement.

Are the lungs the only part of the body that the disease affects?

Not at all necessary. Viral particles are able to infect the cells of the mucous membranes of many organs, primarily the gastrointestinal tract, in the epithelial cells of which there is the same receptor to which the virus attaches as in the cells of the pulmonary epithelium. That is why in some patients the symptoms of infection appear not in the form of cough and pneumonia, but in the form of diarrhea and abdominal pain. This is also confirmed by the fact that coronavirus RNA was isolated in stool samples from patients, although it is still unclear whether the virus can spread in this way. Viral RNA was also found in the blood of patients.

As Dr. Schaffner explained, in principle, when it enters the body, the virus infects all its main organs: the liver, heart, kidneys, as well as bone marrow and blood vessels - and theoretically can cause damage to them.

In addition, if the immune system begins to work at full capacity to fight the infection, organs may fail due to a strong inflammatory reaction.

As a result, in some patients, the damage caused by the body of the virus itself adds damage from the peddling of its own immune system, which threatens fatal consequences.

True, it is still unknown how the infection affects the brain. Scientists who have studied the SARS virus, which causes SARS, have come to the conclusion that in some cases the infection can enter the brain. Given the great similarities between SARS and COVID-19, the authors of a recent publication in the Journal of Medical Virology believe that the risk of nerve cell damage in COVID-19 cannot be ruled out.

Why do some people have a very difficult illness, but most do not?

Approximately 80% of people infected with the new coronavirus have relatively mild symptoms. But the remaining 20% ​​get sick much harder, and for about 2% the disease becomes fatal.

At the same time, the severe course of COVID-19, requiring connection to mechanical ventilation and other life support systems, can be observed in people of all ages, even young and previously completely healthy. Another thing is that such patients are much more likely to survive than the elderly, weakened people, as well as those who suffer from other chronic, systemic diseases, such as diabetes, cancer or chronic obstructive pulmonary disease.

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What do scientists not yet know about COVID-19?

In fact, a lot. Although the disease resembles in many aspects SARS and also has manifestations that are often found with influenza and common pneumonia, specialists still do not fully understand why different patients have different illnesses.

So, the condition of some patients can remain stable for more than a week, and then pneumonia suddenly develops.

Some patients, it would seem, completely recover, and then their symptoms appear again. According to Professor Xiao, he personally knew people whose condition improved to almost normal, and then death suddenly occurred.
In some Chinese patients, the return of symptoms was due to the fact that due to the virus damaged lung tissue, they developed a bacterial infection, and they were dying from it, and not from the virus. But we are talking about individual cases, the reason for the death of most patients is different, said Professor Xiao.

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