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In some patients, the coronavirus may cause loss of smell (known as anosmia). After months of research, scientists discovered the cause of the olfactory problems with COVID-19. It was done by English researchers: rhinologist and ENT surgeon from the University of London Simon Gane and professor of chemistry of flavors Jane Parker.
The most common symptoms of coronavirus infection are fever, dry cough and shortness of breath. One of the common symptoms of infection is also a complete or partial loss of smell (this information has already accompanied the first reports on the course of COVID-19, coming from, among others, Wuhan, and then also from Italy). After months of clinical trials, English scientists were able to determine the reason why patients lose the ability to sense smells, usually for a while.
It is worth emphasizing that problems with the sense of smell are not a symptom that appears in everyone infected with the coronavirus. This symptom alone is therefore not sufficient to confirm SARS-CoV-2 infection.
One of the most common causes of loss of smell (anosmia) are viral infections of the upper respiratory tract, including those caused by coronavirus strains, although usually not causing such serious effects as e.g. COVID-19. In most of these cases, the sense of smell returns once the symptoms subside – the problems with the sense of smell are simply the result of a stuffy nose, preventing the flavor molecules from reaching the olfactory receptors.
- Polish scientists discovered the cause of the loss of smell in the course of COVID-19
As Simon Gane and Jane Parker point out, the pattern of loss of smell in COVID-19 is different. Scientists point out that many people with the coronavirus have reported a sudden loss of smell followed by an equally unexpected full recovery within a week or two. Some said that he did not have a stuffy nose. There were also patients who, despite their recovery, still felt the lack or impairment of their sense of smell for many weeks.
«Now that we have CT scans of the nose and sinuses of coronavirus infected people who have lost their sense of smell, we can see that the part of the nose responsible for perceiving the smells is blocked by swollen soft tissue and mucus. The rest of the nose and sinuses look normal and the patients have no problem breathing through the nose, ‘both scientists found.
Today we know that SARS-CoV-2 infects us by binding to ACE2 receptors on the surface of the cells of the upper respiratory tract. The TMPRSS2 protein helps the virus enter these cells. Once inside, it begins to replicate, triggering an inflammatory response. That’s when the damage to the patient’s body begins – remind Gane and Parker.
Initially, it was thought that the virus would destroy the olfactory neurons. However, studies have shown that the ACE2 receptors needed for the virus to enter cells are not found on their surface. However, they were located on cells that provide structural support for these neurons. Most likely, it is these cells that are damaged by the virus during infection. The reaction causes swelling in a specific area, which disrupts the functioning of the olfactory neurons (but does not directly damage them) and causes loss of smell. After the virus is eliminated, the swelling recedes, aromatic molecules can again freely reach the receptors, and the patient’s sense of smell regains.
- Prof. Butowt: up to 90 percent patients with COVID-19 exhibit changes in smell and taste
Why do some patients regain their sense of smell more slowly?
The explanation is still theoretical and based on the knowledge of inflammation in other body systems. As Gane and Parker explain, inflammation is a defensive reaction in the body, releasing substances to destroy the factors that damage its tissues. «When inflammation is severe, nearby cells begin to be damaged or destroyed (…). This may also apply to the olfactory neurons. In this case, the recovery of the smell takes longer because these neurons need time to regenerate (in such patients the smell may be distorted at first).
Fortunately, olfactory neurons can regenerate. “They grow back in almost all of us all the time,” the researchers say. In their opinion, in regaining the sense of smell, it is worth helping with the physiotherapy of smell, consisting in training the perception of smells. “There is strong evidence that repeated daily exposure to fragrances has a real good effect on loss of smell. There is no reason to believe that it will not work for the loss of COVID-19 odor, »Simon Gane and Jane Parker say.
- Coronavirus symptoms. A sudden loss of smell may indicate a coronavirus infection
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