A team of researchers led by Duke University Medical Center revealed that the failure of some patients to recover their sense of smell following COVID-19 is connected with a persistent immunological attack on olfactory nerve cells and a concomitant loss in the number of those cells.
The study, which was published online on December 21 by the journal Science Translational Medicine, sheds light on a perplexing issue that has affected millions of people whose sense of smell has not entirely returned after contracting COVID-19 (Finlay et al., 2022).
While this study focused on olfactory dysfunction, it provided insight into additional long-term COVID-19 symptoms that the same biological pathways, such as general weariness, shortness of breath, and brain fog, may produce.
According to lead author Bradley Goldstein, M.D., Ph.D., associate professor at Duke’s Department of Head and Neck Surgery and Communication Sciences and Department of Neurobiology, “one of the first symptoms that have traditionally been linked with COVID-19 infection is loss of smell.”
The majority of people whose sense of smell is affected during the acute phase of a viral illness regain their ability to smell within a week or two, but this is not the case for everyone, as Goldstein points out. We need more research into why some persons infected with SARS-CoV-2 go on to experience long-term olfactory dysfunction.
Biopsies of the olfactory epithelium were taken from 24 individuals, nine of whom had had long-term smell loss after contracting COVID-19, and studied by Goldstein and colleagues at Duke, Harvard, and UC San Diego.
The olfactory epithelium, the tissue in the nose where the sense of smell is housed, was examined using this biopsy-based method, which involved the use of advanced single-cell analysis in partnership with Sandeep Datta, M.D., Ph.D., from Harvard University. This unusual inflammatory response continued even when SARS-CoV-2 was not present.
Also, olfactory sensory neurons seemed to be less in number, which may have resulted from inflammation’s wear and tear on the sensitive tissue.
Goldstein remarked, “The results are shocking.” He said that an autoimmune-like process in the nose is “nearly” being resembled.
Goldstein argued that the first stage in developing remedies is to identify the areas of damage and the cell types involved. He added the team was heartened to see evidence that neurons retained some capacity for repair despite the persistent immunological assault.
Goldstein has remarked, “We are hoping that controlling the aberrant immune response or healing mechanisms within the nose of these individuals might assist to at least partially restore a sense of smell.” This study is now being done in his lab.
He also noted that this study’s results could shed light on the inflammatory mechanisms behind other long-lasting COVID-19 symptoms.