Researchers at Duke University Medical Center have discovered why some people take longer to recover their sense of smell after Covid infection. The experts have linked this prolonged loss of smell to an immune assault on olfactory nerve cells, and also to a decline in the number of those cells.
According to the researchers, similar biological mechanisms may be responsible for other long Covid symptoms as well, including brain fog, fatigue, and shortness of breath.
“One of the first symptoms that has typically been associated with COVID-19 infection is loss of smell,” said study senior author Dr. Bradley Goldstein.
“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. 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-CoV-2.”
In collaboration with experts at Duke, Harvard and UC San Diego, Dr. Goldstein analyzed samples from 24 biopsies. Some of the samples were collected from patients who were experiencing long-term loss of smell following Covid infection.
The analysis showed widespread infiltration of T-cells engaged in an inflammatory response in the olfactory epithelium, which is the tissue in the nose where smell nerve cells are located. This inflammation was detected even after the patients tested negative for Covid infection.
Furthermore, the number of olfactory sensory cells had been diminished due to damage from the virus. “The findings are striking,” said Dr. Goldstein. “It’s almost resembling a sort of autoimmune-like process in the nose.”
Learning what sites are damaged and what cell types are involved is a key step toward beginning to design treatments, explained Dr. Goldstein. He said the researchers were encouraged that neurons appeared to maintain some ability to repair even after the long-term immune onslaught.
“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.”
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