Coronavirus symptoms update: The link between loss of sense of smell and COVID-19

Health experts concluded some months ago that a loss of sense of smell and taste could be the best way to predict whether or not a person may have a COVID-19 infection. This is because reports of those symptoms were much stronger in predicting positive COVID-19 diagnosis than self-reported fever. 

Now scientists reveal why a loss of smell may occur when a person is infected with COVID-19

The symptom of loss of smell was only later added to the official list of symptoms despite the large number of people declaring it as a possible warning of an infection.

Scientists have now discovered why coronavirus causes some patients to lose their sense of smell.

Known as anosmia, the temporary loss of smell and sometimes accompanied with loss of taste, is one of the earliest and most commonly reported warning signs of the novel coronavirus.

A new study may have finally uncovered the explanation as to why some COVID-19 patients lose their sense of smell.

Researchers found the ‘hook’ of cells the virus latches onto and infects up to 700 times more in the lining of the upper nose than in the lining of the rest of the nose or that of the windpipe. 

These supporting cells play a vital role in the function and development of odour-sensing cells – and may be damaged when attacked by the pathogen.

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As part of the study, published in the European Respiratory Journal, the researchers looked at nasal tissue specimens from 19 adult men and women with chronic rhinosinusitis, which is inflammation of nasal tissue.

They also looked at tissue samples of the trachea, or the windpipe, from seven people who underwent surgery for abnormal narrowing of the trachea.

These samples were compared to those of four people who had nasal surgeries for issues other than sinusitis. 

They found high levels of ACE2 among nasal cells in an area called the olfactory neuroepithelium, where odour-sensing neurons are located. 

Dr Sandeep Robert Datta from Harvard Medical School said of the findings: “It indicates that the novel coronavirus changes the sense of smell in patients not by directly infecting neurons but by affecting the function of supporting cells.

“I think it’s good news, because once the infection clears, olfactory neurons don’t appear to need to be replaced or rebuilt from scratch.

“We need more data and a better understanding of the underlying mechanisms to confirm this conclusion.”

The researchers noted that cells in the olfactory neuroepithelium had between 200 times and 700 times more ACE2 receptors compared to other samples from the nose and trachea.

Researchers say the findings could lead to the development of drugs, or even a topical cream, to put inside the nostrils that target these cells and cut transmission.

Because the odour-sensing cells had the highest levels of ACE2, the team believes this is why some COVID-19 patients lose their sense of smell. 

The authors say another important takeaway is that the general public needs to not only wear masks but wear them correctly, covering both the nose and the mouth.

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