Covid Smell Loss | Mystery Solved?


A man loses his sense of smell as a result of COVID-19. | Image by Antonio Diaz from Getty Images.

A small study recently published in the journal Science has shed light on the possible mechanism that causes some people to remain without their sense of smell despite having recovered from COVID-19.

Researchers concluded that the illness can prompt an erratic immune response in the olfactory system, despite symptoms having long dissipated.

A lack of sense of smell is a well-known lingering symptom faced by many after contracting COVID-19. Often the sense of smell will return within weeks of the initial infection, according to the study; however, up to 7% of COVID-19 sufferers experience persistent loss of smell for one year or longer.

To uncover the mechanism behind the loss of smell, the researchers took biopsy tissue from the nasal lining of two dozen COVID-19 patients. Nine of the patients experienced smell loss lasting at least four months.

The researchers discovered that the group without smell had T-cells linked to inflammation infiltrating the nasal lining where smell nerve cells are located. Despite this group no longer experiencing COVID-19 symptoms, inflammation persisted, suggesting it lasted even after the infection had passed.

The authors discovered that people with long-term loss of smell possessed fewer olfactory sensory neurons compared to their peers who could smell normally. These cells are responsible for identifying odors and delivering the information to the brain.

According to Brad Goldstein, a study co-author and sinus surgeon at Duke University, on average, patients with a persistent loss of smell maintained only a quarter of the number of neurons compared to those with no issue.

The team suspects “the reduction of sensory neurons is almost definitely related to the inflammation,” said Goldstein.

People suffering from smell loss were also found to possess fewer of a certain type of anti-inflammatory cell and more of a certain type of inflammatory cell than their healthy counterparts.

The findings help support the theory that “long Covid” symptoms could be caused by inflammation. A previous study discovered that people who succumbed to COVID-19 had discernable inflammation in the olfactory bulb, the region of the brain that communicates with the olfactory sensory neurons in the nose.

Dr. Cheng-Ying Ho, a co-author of the previous study and associate professor of pathology at Johns Hopkins University School of Medicine, said inflammation originating in the nasal cavity could very well travel to the brain. While the new results are compelling, according to Dr. Ho, more research is needed to expand on the small sample size of 24 patients.

A 2021 survey of over 400 patients who lost their sense of smell found that more than four out of 10 experienced depression, and nearly nine out of 10 reported enjoying food less.

“People might think smell loss is not really an important Covid symptom compared with severe symptoms such as pneumonia, but it can really bother some patients,” said Dr. Ho.

At this time, no effective treatments exist for people suffering from a loss of smell, said Dr. Sandeep Robert Datta, one of the study’s co-authors and a professor of neurobiology at Harvard Medical School.

“Smell gives you a sense of place. It can be very disorienting without it,” he said.

COVID-19 infection more severely affects people with other conditions, such as those who are obese, studies show. Obesity is one of the most significant health problems facing the nation and the state, with Dallas ranking as one of the most obese major U.S. cities.

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