We may finally know why some people’s sense of smell doesn’t recover after COVID: ScienceAlert

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

The SARS-CoV-2 infection prompts a sustained attack by the immune system on nerve cells in the nose, a new study finds, and then the number of nerve cells decreases, leaving people unable to smell and smell as they normally would.

In addition to answering the question that has baffled experts, the research 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 recover their sense of smell within the next week or two, but some do not,” says neurobiologist Bradley Goldstein from Duke University in North Carolina.

“We need to better understand why this subgroup of people will have persistent loss of smell months to years after being infected with SARS-CoV-2.”

The team studied samples of nasal tissue – the olfactory epithelium – taken from 24 people, including nine with long-term loss of smell after recovering from COVID-19. This tissue holds the neurons responsible for smell detection.

After detailed analysis, the researchers observed a widespread presence of T-cells, a type of white blood cell that helps the body fight infection. These T-cells started an inflammatory reaction inside the nose.

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

“The discoveries are astonishing,” says Goldstein. “It almost resembles some kind of 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 report that some neurons appear to be able to repair themselves even after being bombarded with T cells—an encouraging sign.

The researchers suggest that similar inflammatory biological mechanisms may be behind other symptoms of long-term 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 areas of tissue are damaged and what types of cells are involved. This in turn will lead to the development of possible treatments for those with long-term loss of smell.

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

The research was published in Science translational medicine.