US scientists have discovered that some people do not regain their sense of smell after being infected with SARS-CoV-2 because the virus causes continued immune aggression that depletes the number of olfactory nerve cells.
The finding, published this Wednesday in the journal Science Translational Medicine, finally explains how a problem that affects millions of people around the world occurs.
The research also sheds light on the possible underlying causes of other prolonged symptoms of covid-19, such as general fatigue, shortness of breath or lack of concentration, which could be triggered by similar biological mechanisms, according to the researchers.
“One of the first symptoms often associated with covid-19 infection is loss of smell. Fortunately, many people regain their sense of smell in a week or two, but others do not,” says Bradley Goldstein, lead author of the study. and Neurobiology researcher at Duke University (North Carolina, United States).
“We wanted to better understand why some people have persistent loss of smell for months or years after being infected,” he explains.
Together with scientists from Harvard and the University of California-San Diego, the Duke team analyzed olfactory epithelial samples collected from 24 biopsies, including those from nine patients with persistent loss of smell.
The analysis showed widespread infiltration of T cells involved in an inflammatory response in the olfactory epithelium, the tissue in the nose that contains the nerve cells for smell.
The inflammatory process persisted after infection and the number of olfactory sensory neurons was reduced, possibly due to damage to delicate tissue sustained by persistent inflammation.
For Goldstein, “the results are amazing. It almost looks like some kind of autoimmune process in the nose.”
Goldstein believes that knowing which areas are damaged and which types of cells are involved is key to beginning to design treatments.
Furthermore, the team finds it encouraging that neurons appear to retain some capacity for repair even after immune attack.
“We are hopeful that modulating abnormal immune response or repair processes in the nose of these patients may help restore, at least in part, their sense of smell,” he says.
In his opinion, the results of this study could also be helpful for further research on other long-lasting symptoms of covid-19 that could be caused by similar inflammatory processes.