(It’s common knowledge that having COVID-19 can affect your sense of smell, but in some cases, that olfactory function doesn’t return properly. Now new research explains why.
SARS-CoV-2 infection causes an ongoing attack by the immune system on nerve cells in the nose, new study says, and there is then a drop in the number of those nerve cells, leaving people unable to smell and smell as they usually would .
In addition to answering a question that has baffled experts, the research could also help our understanding of long-term COVID and why some people fail to fully recover from COVID-19.
“Fortunately, many people who have an impaired sense of smell during the acute phase of viral infection will recover their sense of smell within the next week or two, but some do not,” says neurobiologist Bradley Goldstein from Duke University in North Carolina.
“We need to better understand why this subset of people will continue to have a persistent loss of smell for months to years after being infected with SARS-CoV-2.”
The team studied samples of nasal tissue – olfactory epithelium – taken from 24 people, nine of whom experienced long-term loss of smell after contracting COVID-19. This tissue contains the neurons responsible for detecting odors.
After a detailed analysis, the researchers observed the widespread presence of T cells, a type of white blood cell that helps the body fight infections. These T cells were driving an inflammatory response within the nose.
However, as with many other biological responses, T cells apparently do more harm than good and damage olfactory epithelial tissue. The inflammatory process was still evident even in tissues where SARS-CoV-2 was not detected.
“The results are amazing,” says Goldstein. “It almost looks like some sort of autoimmune process in the nose.”
While the number of olfactory sensory neurons was lower in study participants who lost their sense of smell, the researchers report that some neurons appear able to repair themselves even after T-cell bombardment, an encouraging sign.
The researchers suggest that similar inflammatory biological mechanisms may underlie the other symptoms of long-term COVID, including excessive fatigue, shortness of breath and a “brain fog” that makes it difficult to concentrate.
Next, the team wants to look in more detail at which particular areas of tissue are damaged and which cell types are affected. This, in turn, will pave the way for the development of possible treatments for those suffering from a long-term loss of smell.
“We hope that modulating the abnormal immune response or repair processes within the nose of these patients could help to at least partially restore the sense of smell.” says Goldstein.
The research was published in Science Translational Medicine.
