We may finally understand why some people don’t recover their sense of smell after COVID: ScienceAlert

We may finally understand why some people don’t recover their sense of smell after COVID: ScienceAlert

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(It is well known that owning COVID-19 can affect your sense of smell, but in some cases this olfactory function does not recover properly. Now, new research explains why.

The SARS-CoV-2 the infection triggers an ongoing immune system attack on nerve cells in the nose, the new study says, and then there’s a decline in the number of those nerve cells, leaving people unable to sniff and smell as normal.

In addition to answering a question that has puzzled experts, the study may also help our understanding long covid and why some people cannot fully recover from COVID-19.

“Fortunately, many people who have an altered sense of smell during the acute phase of a viral infection will regain their sense of smell within the next one to two weeks, but some do not,” says neuroscientist Bradley Goldstein from Duke University in North Carolina.

“We need to better understand why this subset of people will continue to have persistent loss of smell for months to years after contracting SARS-CoV-2.”

The team examined samples of nasal tissue – the olfactory epithelium – taken from 24 people, including nine who had long-term loss of smell after getting through COVID-19. This tissue holds the neurons responsible for detecting smells.

After detailed analysis, the researchers observed the widespread presence of T cells, a type of white blood cell that helps the body fight infection. These T cells trigger an inflammatory response in the nose.

However, as in many other biological reactions, T cells apparently do more harm than good and damage the olfactory epithelial tissue. The inflammatory process was still evident even in tissue where SARS-CoV-2 was not detected.

“The findings are striking,” says Goldstein. “It almost looks like an autoimmune process in the nose.”

Although the number of olfactory sensory neurons was lower in the study participants who lost their sense of smell, the researchers reported that some neurons appeared to be able to regenerate even after the T-cell bombardment—an encouraging sign.

Researchers suggest that similar inflammatory biological mechanisms may be behind other symptoms of prolonged COVID, including excessive fatigue, shortness of breath, and “brain fog” that makes it difficult to concentrate.

Next, the team wants to look in more detail at which specific tissue areas are damaged and which types of cells are involved. This in turn will lead to the development of possible treatments for those experiencing long-term loss of smell.

“We hope that modulating the abnormal immune response or repair processes in the nose of these patients may help to at least partially restore the sense of smell,” says Goldstein.

The study was published in Scientific Translational Medicine.

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