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How the coronavirus attacks our entire body

A lesson in humility. This is probably what strikes you the most when listening to doctors confronting patients suffering from severe forms of Covid-19.

Because the more the weeks pass, the more the pathology induced by the SARS-CoV-2 virus seems to show new faces, sometimes completely unexpected. We knew its ability to attack the lungs, now we discover its ability to cause neurological, cerebral, digestive, renal, hepatic, cardiac, but also vascular damage.

“This disease can attack almost anything in the body with devastating consequences. His ferocity is breathtaking, “says Yale Harlan Krumholz University cardiologist in the magazine Science, in a particularly extensive article on the harmful consequences of the virus.

As a caregiver, it feels like you are thirty years back when AIDS first emerged

Alexandra Calmy, specialist in infectious diseases at HUG

No “pattern”

Despite a very dense scientific literature – more than 1,000 articles related to Covid-19 already published or pending on pre-print servers -, researchers are still struggling to understand how the virus attacks cells in the body, especially in the 5% of patients who fall seriously ill.

“Sometimes we have to explain to patients that we don’t yet know all of the possible clinical manifestations of this disease. As a caregiver, it feels like you’re back thirty years ago when AIDS emerged, says Alexandra Calmy, an infectious disease specialist at Geneva University Hospitals. The symptoms can be very different from one patient to another, and we often move away from classic viral pneumonia. This is why we must remain vigilant during our clinical assessments. “

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Effects on the lungs and heart…

What are the observed effects of SARS-CoV-2 on our different organs? Those induced on the respiratory system are now well known. If the viral invasion is not repelled by the immune system during the initial phase of the disease, the virus can reach the lungs and attack the alveoli, where gas exchanges take place between the body and the outside air.

“The immune system’s battle against the invader can itself disrupt healthy oxygen transfer,” the authors write. Science in their article. Front-line white blood cells release inflammatory molecules, which in turn invoke more immune cells that target and kill virus-infected cells, leaving behind a mass of dead cells and pus. ”

These lesions are the famous frosted glass stains that can be seen on the scanners of patients with Covid-19. Faced with this phenomenon, some people develop an acute respiratory distress syndrome (ARDS), which can lead to death in severe cases.

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On the cardiovascular side, attacks of SARS-CoV-2 also seem to be frequent. A study published on March 25 in JAMA Cardiology covering 416 patients hospitalized in Wuhan, documented heart damage in almost 20% of patients. Among those admitted to intensive care, it also appears that arrhythmia (disturbance of the heart rhythm) but also the formation of blood clots are particularly frequent, which can potentially lead to pulmonary embolism when the latter migrate in the lungs or strokes when they get lodged in the brain.

… But also on the kidneys, the brain and the digestive tract

Kidney failure has been observed in a large percentage – between 30 and 60% depending on the study – of hospitalized patients. Results of autopsies conducted in China indicate that the virus could attack the kidneys directly, but kidney damage could also be caused by prolonged use of respirators or, more rarely, by taking antiviral drugs like Remdesivir .

Observations also suggest that between 5 and 10% of Covid-19 patients suffer from neurological disorders, with the appearance of cerebral inflammatory encephalitis, convulsions, loss of consciousness, or loss of taste or of smell. Up to a third of patients also suffer from conjunctivitis.

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Finally, there is evidence to show that the new coronavirus is capable of infecting the lining of the lower digestive tract. Viral RNA was thus found in more than 50% of the stool samples of the patients tested. Between 20% and 50% of those infected are said to suffer from diarrhea, symptoms that are sometimes overlooked by healthcare professionals when seeking a Covid-19. Finally, liver damage has also been observed in some patients, although experts have not yet been able to say which virus, antiviral drugs or over-inflammation of the immune system is the real culprit.

Gateway to the virus

How to explain the variety of effects caused by the SARS-CoV-2 virus? For many scientists, one of the keys to this phenomenon is an enzyme called ACE2 or angiotensin II converting enzyme. It is indeed on this cellular receptor that SARS-CoV-2 binds, using the spicules located on its surface, to enter the cells.

Much more than pneumonia, Covid-19 is a systemic inflammation of the blood vessels

He can then hijack their internal machinery in order to create a myriad of copies of himself, before the latter invade new cells. According to a pre-impression study conducted by French, English and Dutch scientists, the new coronavirus would find particularly favorable ground, as soon as it enters the body, within the mucous membrane of the nose, whose epithelial cells are particularly rich in ACE2.

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Involved in the control of blood pressure, the ACE2 receptors are also present on the external face of the cell membranes of the lungs, arteries, heart, kidneys and also of the digestive system where these enzymes are particularly numerous, but also in the neural cortex and the brainstem, which could explain the diversity of the symptoms encountered.

Systemic inflammation

This hypothesis is supported in research published on April 20 in The Lancet by researchers from the University of Zurich. By examining tissue samples from deceased patients under a microscope, they found that the inflammation affected the endothelium – the inner lining of blood vessels – of different organs. The penetration of SARS-CoV-2 into the endothelium would most likely be through the ACE2 receptors, which are found in number.

“Much more than pneumonia, Covid-19 is a systemic inflammation of the blood vessels. It causes serious micro-disturbances in the blood circulation that can damage the heart or cause pulmonary embolism, or even block blood vessels in the brain or the gastrointestinal system, “the institution said in a statement.

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This discovery could explain the disparities between individuals facing the new coronavirus. “While the endothelium of young people defends themselves well, this is not the case for the risk groups suffering from hypertension, diabetes or cardiovascular disease, the common characteristic of which is reduced endothelial function”, write Zurich experts. What to think about new therapeutic avenues that would combine both the fight against the multiplication of the virus and the protection of the vascular system of patients.

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