Angela Onwuzoo
Scientists have explained the reasons why some COVID-19 survivors fail to recover their sense of smell years after recovering from the disease.
The scientists in a new study linked the loss of smell to an ongoing immune assault on olfactory nerve cells and an associated decline in the number of those cells.
According to them, the inflammatory mechanism could also help explain other long COVID-19 symptoms.
The study published in ScienceDaily, scientists say provides an important insight into a vexing problem that has plagued millions who have not fully recovered their sense of smell after COVID-19.
Many sufferers describe the loss as extremely upsetting, even debilitating, all the more so because it is invisible to others.
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 might be triggered by similar biological mechanisms.
Senior author of the study and Associate Professor of Head and Neck Surgery & Communication Sciences, Department of Neurobiology, Duke University Medical Center, North Carolina, United States, Dr. Bradley Goldstein said one of the first symptoms that have typically been associated with COVID-19 infection is loss of smell.
“Fortunately, many people who have an altered sense of smell during the acute phase of viral infection will recover the smell within the next one to two weeks, but some do not.
“We need to better understand why this subset of people will go on to have persistent smell loss for months to years after being infected with SARS-CoV2,” Goldstein said.
In the study, Goldstein and colleagues at Duke, Harvard, and the University of California-San Diego analysed olfactory epithelial samples collected from 24 biopsies, including nine patients suffering from long-term smell loss following COVID-19.
The scientists explained that using a biopsy-based approach, a sophisticated single-cell analysis 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.
According to them, this unique inflammation process persisted despite the absence of detectable SARS-CoV-2 levels.
Additionally, the scientists noted that the number of olfactory sensory neurons was diminished, possibly due to damage to the delicate tissue from the ongoing inflammation.
Goldstein further said, “The findings are striking. It’s almost resembling a sort of autoimmune-like process in the nose. 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 learning what sites are damaged and what cell types are involved is a key step toward beginning to design treatments. He said the researchers were encouraged that neurons appeared to maintain some ability to repair even after the long-term immune onslaught.
He said the findings from the study could also inform additional research into other long-COVID-19 symptoms that might be undergoing similar inflammatory processes.
Scientists had in 2020 warned that many survivors of COVID-19 who lost their senses of taste and smell may not recover those senses after other symptoms of the disease might have disappeared.
According to preliminary data from clinicians, about a quarter of recovered COVID-19 patients say they regained their senses of taste and smell within two weeks of other symptoms disappearing.
Researchers, however, said long-term data is needed to determine when those who did not report an improvement in two weeks recovered their ability to taste and smell.
“It could take months, and some physicians say they may never recover those senses,” the scientists warned; adding, “This may put up more barriers to full recovery for COVID-19 patients, causing emotional distress and anxiety.”
Speaking in an interview with Reportr Door HealthWise on the issue, Chief Executive Officer, of the Institute of Human Virology Nigeria, Dr. Patrick Dakum said it is expected that the loss of taste and smell senses will clear after the infection is cleared, urging survivors still experiencing the symptom to exercise patience.
Dr. Dakum noted that inflammatory changes in the sensory organs might be responsible for the loss of taste and smell.
The public health physician said, “It’s not clear why it doesn’t affect all but individual antibody responses may account for the difference.
“These are still being studied. It’s expected that this will clear after the infection is cleared.
“The length of time these symptoms will last is not clearly defined.
“Remember, we are still on a learning curve as far as COVID-19 is concerned. Patients should patiently wait until symptoms clear.”
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