A team of scientists led by Duke Health report revealed that people who do not recover their sense of smell after Covid-19 are due to an ongoing immune assault on olfactory nerve cells and an associated decrease in the number of those cells. Published online in the journal Science Translational Medicine, the finding provides an important insight into the mass problem affecting millions around the globe.
While focusing on the loss of smell, the finding also sheds light on the possible underlying causes of other long Covid-19 symptoms including generalised fatigue, shortness of breath, and brain fog that similar biological mechanisms might trigger. Senior author Bradley Goldstein, M.D., Ph.D., associate professor in Duke’s Department of Head and Neck Surgery and Communication Sciences and the Department of Neurobiology.
Goldstein said, “Fortunately, many people with an altered sense of smell during the acute phase of viral inflection 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 continue to have persistent smell loss for months to years after being infected with SARS-CoV2.”
Researchers analysed olfactory epithelial samples collected from 24 biopsies, including nine patients suffering from long-term smell loss following Covid-19. The biopsy-based approach, using sophisticated single-cell analyses in collaboration with Sandeep Datta, M.D, Ph.D., at Harvard University, revealed widespread infiltration of T-cells engaged in an inflammatory response in the olfactory epithelium, the tissue in the nose where smell nerve cells are located.
Additionally, the number of olfactory sensory neurone were diminished, possibly due to damage to the delicate tissue from the ongoing inflammation. “The findings are striking. It’s almost resembling a sort of autoimmune-like process in the nose,” Goldstein said. He said learning what sites are damaged and what cell types are involved is a key step toward beginning to design treatments. He added that the researchers were encouraged that neurone 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,” Goldstein said.