One-Third of Coronavirus Patients Lose Sense of Smell

There have been reports this week in the media that 30% of patients of coronavirus are facing anosmia (loss of smell).

Charles Greer, professor of neurosurgery and neuroscience at Yale School of Medicine (YSM), and director of the interdepartmental neuroscience graduate program, and has studied human olfactory system for a long time, was intrigued by this and decided to study what part of the virus is causing the problem or how it is  manifesting.

Source: Springer Link

Very little is known about the virus and it is not easy to understand it. There are many questions that need to answered, like are the neurons of the nose degenerating or are they destroyed by the virus? Why is a virus attacking the cells? Why not the cells of skin or eyes?

There are special cells, called hair cells, in the olfactory tract that respond to particular chemicals. These cells have small hairs called cilia on one side and an axon on the other side. The electrical activity produced in these hair cells is sent to the olfactory bulb.

COVID-19 is very much fond of lung cells and it attacks them. The scientists realized that the same cells are found on the epithelium of nose which is the layer containing neurons responsible for the sense of smell. The olfactory tract transmits the signals to the brain.

Greer says: “The public reports describe patients regaining their sense of smell very quickly after recovery. It is interesting because the olfactory epithelium can regenerate quickly — there’s an almost complete turnover in cellular material there every 6-8 weeks. The olfactory epithelium is the only sensory system that’s directly connected to the brain. Other senses — touch, taste, auditory, sight — are all mediated by additional mechanisms that interpret signals and pass them along through the nervous system to the brain. The smell is processed by the same neurons that extend into the brain.”

As some scientists are working on the COVID-19 effects on neurologic functions, others are working on measuring the loss of smell. Dr. Dana Small, professor of psychiatry and professor of psychology, and director Modern Diet and Physiology Research Center, has started a research on people to measure their ability of smell while infected with COVID-19.

She and her colleagues have made a device to measure the loss of smell over time and started by using common items found in the home. They used peanut butter to check the strength of smell. She believes that peanut butter is a strong stimulus and is easily found at homes. Peanut butter has been used by other scientists as well to measure the sense of smell in Alzheimer’s disease.

Dana Small says olfactory loss is not uncommon with other viruses, but the smell is one of those things we take for granted and tend not to notice until it’s gone.

Small believes that usually when people complain about their sense of smell, their sense of taste declines as well. It doesn’t occur because of the inability to differentiate between sweet and sour, it is because of the decline in retronasal olfactory function. The community of chemosensory is working to help amid this crisis.

Greer proves her point by explaining that when one closes the nose and eats the strawberry, one can only differ particular elements but when the nose is opened and air flows in, one can feel a new experience that links with taste.

Loss of smell in COVID-19 patients could help in differentiating the asymptomatic patients from the healthy ones.

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