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Mysteries of COVID Smell Loss

Reported : Irina  Robu, PhD

When Covid-19 patients have smell loss it tends to be sudden and severe. They are usually don’t have a blocked, stuffy or runny nose – most people with coronavirus can still breathe freely.  Since the epidemy started in march, an estimated of 80 percent of people with COVID-19 have experience smell disturbances in addition to loss of taste and the ability to smell chemical irritants. Research has shown that smell loss is common in people with COVID-19 disease, the reason why researchers and doctors have recommended to use a diagnostic test to determine if a patient has COVID-19.

Yet, the mystery is how the new coronavirus robs patients of their senses. During the early days of the epidemic, physicians and researchers thought that COVID related loss of smell might signal that the virus makes its way into the brain through the nose, where it can do the most severe damage. According to Sandeep Robert Data, a neuroscientist at Harvard Medical School, the research data showed that the primary source is the in the nose, but more specifically in the nasal epithelium. It looks like the virus attacks the cells responsible for registering odors rather than attacking neurons directly.  

It is well known that  olfactory neurons do not have angiotensin-converting enzyme 2 (ACE2) receptors, which permit the virus entry to cells, on their surface. But sustentacular cells, which provide support for  olfactory neurons are scattered with the receptors. These cells preserve the important  balance of salt ions in the mucus that neurons rest on on to send signals to the brain. If that balance is disturbed, it could lead to a closure of neuronal signaling and loss of smell.

The sustentacular cells correspondingly deliver the metabolic and physical support necessary to keep the fingerlike cilia on the olfactory neurons wherever receptors that detect odors are disturbed. Nicolas Meunier, a neuroscientist at the Paris-Saclay University in France determined that disruption of the olfactory epithelium might explain the loss of smell. Yet, it remains unclear if the damage done by the virus or because it invades immune cells.

Since COVID-19 doesn’t cause nasal congestion, researchers have found a few clues about the loss of smell. Taste receptor cells, which detect chemicals in the saliva and sends signals to the brain do not have ACE receptors. They don’t necessarily  get infected by COVID-19, but other support cells in the tongue carry the receptor.

Researchers determined that more clues on  to how the virus obliterates smell. However, some patients have seen that after five months the ability to smell has returned but not as great as expected. That news is welcomed for patients that have suffered loss of smell due to the COVID-19 virus, yet apprehensions about long term loss of smell is a large cause of concern.

SOURCE

https://www.scientificamerican.com/article/mysteries-of-covid-smell-loss-finally-yield-some-answers1/

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