Scientists have finally discovered one of the secrets of COVID-19: why the sense of smell disappears

According to sciencealert.com, one of the leading causes of olfactory loss is a viral infection with colds, sinusitis, or another upper respiratory tract infection. Coronaviruses, which do not cause fatal diseases, have been known in the past as one of the causes of the common cold, and often cause loss of smell.

In most cases, the sense of smell returns on its own when the symptoms of the disease disappear, since most often the smell disappears due to nasal congestion, so the odor molecules cannot reach the receptors olfactory from the nose. In some cases, the odor can go away for months or even years.

However, in the case of the new coronavirus, olfactory loss is different. Many infected with the virus said the odor abruptly disappeared and returned after a week or two. And most interestingly, many people indicated that their noses were not clogged, so the loss of smell cannot be explained by that.

For some people, the smell disappeared for a long time and they couldn’t smell anything even after a few weeks. And any theory to explain the anosma caused by COVID-19 must take into account these two factors.

The sudden return of odor suggests that it is still an obstructive loss of smell when odor molecules cannot reach receptors in the nose.

Computed tomography results of the nose and sinuses of people infected with COVID-19 show that inflamed tissues and mucus are formed in the nose area responsible for smell, and the rest of the nose and sinuses are normal. , allowing patients to breathe normally through the nose.

The new coronavirus is already known to infect the body by attacking ACE2 receptors on cells that line the upper respiratory tract. And a protein called TMPRSS2 helps the virus infect cells.

Once in the cell, the virus begins to multiply and triggers an anti-inflammatory attack by the immune system. This is the beginning of the chaos and destruction caused by the virus in the body.

Initially, the virus was thought to be likely to infect and destroy olfactory neurons, cells that transmit a signal from an odor molecule in the nose to a location in the brain that interprets that signal as odor.

However, an international study recently showed that the ACE2 proteins that the virus needs to infect cells are not present in olfactory neurons. But they have been found in cells called “support cells” that support olfactory neurons.

The researchers believe that the virus is more likely to damage these cells, and the immune response increases the part that contains olfactory neurons that remain intact. When the immune system copes with the virus, the swelling disappears and the odor molecules reopen to healthy olfactory receptors, returning the person to a normal sense of smell.

But why in some cases does the sense of smell return? It is already possible to speculate and put forward various theories here, but it is known about inflammation in other systems. Inflammation is the body’s response to injury that causes the body to release certain chemicals that destroy damaged tissue. In cases where the inflammation is severe, those chemicals also begin to destroy nearby healthy tissue. This is believed to be the second stage in which olfactory neurons are damaged.

Perfume recovery becomes much slower because it takes time for neurons to regenerate from stem cells in the nasal mucosa.

The initial stage of recovery is often associated with a distorted sense of smell called parosmia, when various things smell at all like they once smelled. For example, for many patients exposed to parosmia, coffee is released from flammable substances, chemicals, dirt, and sewage.

Physiotherapy for the nose.

Scent is often referred to as Cinderella Physiology because little research has been done in this area. However, following the coronavirus pandemic, this area has received additional attention, making it possible to learn a great deal about how viruses work. So what can people who have lost their sense of smell expect from the current situation?

The good news is that olfactory neurons are regenerating. They grow back in virtually everyone, and it’s happening all the time. And we can speed up this process. perform a kind of nasal physiotherapy: olfactory training.

There is strong evidence that many forms of olfactory loss can be treated daily by deliberately sniffing a particular set of fragrances, and there is no reason to believe that such therapy would not help COVID-19 patients who have lost their sense of smell.