A new study explains the loss of sense of smell in people infected with the Corona virus

Weather of Arabia - The loss of the sense of smell is one of the most common symptoms among those infected with the Corona virus (before the emergence of the mutant Omicron), as it was among the 10 most common symptoms, but this has changed since the rapid spread of Omicron, which witnessed a clear decrease in the rate of loss of smell to about One in five people tested positive. But it remains the most unusual symptom of coronavirus infection, and a topic of research for scientists.

And in a new study published on February 2 in the journal Cell, it was found that infection with the emerging coronavirus indirectly reduces the action of olfactory receptors (OR), proteins on the surfaces of nerve cells in the nose that detect molecules related to odors.

Led by researchers from New York University School of Medicine and Columbia University, the new study also sheds light on the effects of COVID-19 on other types of brain cells, and on other ongoing neurological effects of coronavirus infection, such as "brain fog," headaches and depression.

Experiments showed that the presence of the virus near neurons in the olfactory tissues triggered an eruption of immune cells, microglia and T cells, which sense and fight infection. These cells release proteins called cytokines that alter the genetic activity of olfactory neurons, even though the virus cannot infect them, the study authors say, but immune signals persist in a way that reduces the activity of genes needed to build olfactory receptors.

A weak sense of smell is one of the most common effects we see with seasonal upper respiratory infections, where the common symptoms of nasal congestion and runny nose lead to poor airflow and reduced delivery of odors to the area of the nose responsible for smell, but researchers in this study showed that one of the unique symptoms of a virus infection Corona is the loss of the sense of smell without a stuffy nose that appears with other infections such as the common cold.

In most cases, the loss of smell lasts only a few weeks, but for more than 12% of COVID-19 patients, the olfactory impairment persists in the form of a persistent decrease in the ability to smell or changes in how a person perceives the same smell (parosmia).

To get an explanation for this, the study authors explored the molecular consequences of MERS infection in golden hamsters and in olfactory tissues from 23 human autopsies. Hamsters are a good model, being mammals that rely more on their sense of smell than humans, and are more susceptible to infections of the nasal cavity.

In the olfactory neuron tissue of both hamsters and humans, the research team discovered a persistent and widespread downregulation of olfactory receptor synapsis. Other work published by these authors indicates that olfactory neurons are connected to sensitive brain regions, and that persistent immune cell interactions in the nasal cavity can influence emotions and the ability to think clearly (perception), which is consistent with the long-term symptoms of Covid infection.

Hamster experiments showed that downregulation of olfactory neuron receptors persisted after short-term changes that might affect the sense of smell had recovered normally. The authors say this suggests that COVID-19 causes a long-term disruption of the chromosomal regulation of gene expression, a form of "nuclear memory" that can prevent transcription recovery even after recovery from the virus.

In the next step, the team is investigating whether long-term treatment of hamsters with COVID-19 with steroids can reduce harmful immune reactions (inflammation) to protect the nuclear structure. We hope that researchers will find results that benefit patients who have weak or lost their sense of smell after recovering from the virus.