Many who have been infected with the Coronavirus have a modified sense of smell, and in some cases this sense of smell has not returned properly to its previous state.
The new study, published in the journal Science Translational Medicine, indicates that SARS-CoV-2 infection consistently attacks the immune system on nerve cells in the nose, causing a decrease in the number of those nerve cells and making people unable to smell like they normally do.
In response to a question that has puzzled experts, neuroscientist Bradley Goldstein, of Duke University in North Carolina, says: “Fortunately, many people who have a modified sense of smell during the acute phase of a viral infection will regain it by the next week or two, but some don’t. “We need to better understand why this subset of people will continue to lose their sense of smell for months and even years after infection with SARS-CoV-2.”
For this reason, a medical team studied nasal tissue samples taken from 24 people, including nine who suffered from long-term loss of smell after being infected with “Covid-19”. This tissue carries the nerve cells responsible for detecting odors.
Upon detailed analysis, the researchers noted the widespread proliferation of T cells, a type of white blood cell that helps the body fight infection. These T cells were driving an inflammatory response within the nose.
And the medical team found that T cells do more harm than good, as they damage olfactory epithelial tissue, and they also found that the inflammatory process is still evident even in tissue where SARS-CoV-2 has not been detected.
“The results are amazing,” says Goldstein, “it’s almost like some sort of autoimmune process in the nose.”
And while the number of olfactory sensory neurons was lower in study participants who lost their sense of smell, the researchers reported that some neurons appeared to be able to repair themselves even after T-cell bombardment, an encouraging sign.
The researchers suggest that similar inflammatory biological mechanisms may underlie other long-lasting coronavirus symptoms, including excessive fatigue, shortness of breath and ‘brain fog’ that makes it difficult to concentrate.
The team set out to investigate in more detail the specific areas of tissue that were damaged and the cell types involved, which could lead to the development of potential treatments for those suffering from long-term loss of smell.
“We hope that modifying the abnormal immune response or repairs within the noses of these patients will help at least partially restore their sense of smell,” says Goldstein.
