[NewsQuest = Science Reporter Kim Hyung-geun]Loss of smell is a representative symptom among the sequelae of COVID-19 infection. However, this symptom lasts for quite a long time depending on the person. Why?
Researchers at Duke University Medical Center in North Carolina, USA, have discovered why it takes longer for some people to regain their sense of smell following contracting COVID-19.
They concluded that the reason for this long-term loss of smell was an immune attack on the olfactory neurons, followed by a decrease in olfactory cells.
Because of immune attack, olfactory cells are reduced
According to the research team, it may be the cause of other long Covid symptoms, including brain fog, fatigue and shortness of breath caused by COVID-19 infection.
Professor Bradley Goldstein, who led the study, said: “Usually, one of the first symptoms associated with COVID-19 infection is loss of smell.”
“Fortunately, many people who had an altered sense of smell recovered within a week or two during the height of the COVID-19 virus infection, but some did not. We wanted to know more regarding why some of these people had a persistent loss of smell for months or years. You need to understand it well,” he explained.
Goldstein’s team, in collaboration with experts from Harvard University and the University of California, San Diego, analyzed 24 biological samples. Some of the samples were collected from patients suffering from long-term loss of smell following being infected with COVID-19.
As a result of the analysis, it was found that T cells involved in the inflammatory response had extensively infiltrated the olfactory epithelium, a tissue inside the nose where olfactory nerve cells are located. The inflammation was detected even following the patients tested negative for COVID-19.
‘Long Covid’ symptoms such as brain fog, fatigue and shortness of breath are also partly to blame
Moreover, viral damage reduced the number of olfactory cells.
“This finding is surprising,” Goldstein said. “It’s very similar to a process like autoimmunity in the nose.”
Originally, the immune cells of our body respond to foreign substances when they invade. In this process, an inflammatory response occurs.
An autoimmune disease is a disease that occurs when the immune system of our body attacks the cells of our body, not foreign substances, for some reason. Allergies are a prime example.
Figuring out which areas are damaged and which cell types are involved is a key step to begin designing therapies, Dr. Goldstein explained.
He said the team was encouraged by the fact that neurons seem to retain the ability to recover following a prolonged immune attack.
“We suspect that modulating an abnormal immune response or repair process within the nose of these patients may help restore their sense of smell, at least in part,” he concluded.