Covid-19: Here’s why patients lose their sense of smell

Following Covid-19, some patients do not regain their sense of smell because of a persistent immunological attack on their olfactory nerve cells resulting in a reduction in the number of these cells, according to a paper by a group of researchers lead by Duke Health.

This result, published online in Science Translational Medicine on December 21, sheds light on a perplexing issue that has afflicted millions of people whose sense of smell has not entirely restored after Covid-19.

While the study's primary emphasis was on olfactory dysfunction, its findings also provided insight into the potential molecular processes behind the other extended Covid-19 symptoms, such as generalised weariness, shortness of breath, and brain fog.

"One of the first symptoms that has typically been associated with Covid-19 infection is loss of smell," said senior author Bradley Goldstein, M.D., Ph.D., a Duke associate professor. "Fortunately, many people who have an altered sense of smell during the acute phase of viral infection will recover smell within the next one to two weeks, but some do not," he said. 

"We need to better understand why this subset of people will go on to have persistent smell loss for months to years after being infected with SARS-CoV2," he added.

Olfactory epithelium tissues from 24 biopsies, including 9 individuals with long-term smell loss after Covid-19, were analysed by Goldstein and colleagues at Duke, Harvard, and UC San Diego.

The olfactory epithelium, which houses the nerve cells responsible for detecting odours, was the target of this biopsy-based method, which used advanced single-cell studies in partnership with Sandeep Datta, M.D., Ph.D. of Harvard University. A lack of measurable SARS-CoV-2 levels did not prevent this unusual inflammatory process from continuing. Olfactory sensory neurons also decreased in number, which may have been caused by inflammation's impact on the fragile tissue.

"The findings are striking," Goldstein said. "It`s almost resembling a sort of autoimmune-like process in the nose."

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The first stage in therapy development, according to Goldstein, is to identify the areas of damage and the cell types implicated. He added the team was heartened by the fact that neurons showed signs of being able to repair themselves despite the persistent immunological assault.

"We are hopeful that modulating the abnormal immune response or repair processes within the nose of these patients could help to at least partially restore a sense of smell," Goldstein explained.

He said that the study's results might potentially shed light on the investigation of other chronic Covid-19 symptoms that may be influenced by comparable inflammatory mechanisms.

(With inputs from ANI)