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Why did COVID-19 take my sense of smell?

New research reveals the mechanism that leads to loss of smell from COVID-19.

woman trying to smell coffee but COVID-19 leaves some with no sense of smell

The study was led by by researchers from NYU Grossman School of Medicine and Columbia University.


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So why can’t I smell?

The study found that the COVID-19 virus indirectly dials down the action of olfactory receptors. These are proteins on the surfaces of nerve cells in the nose that detect the molecules associated with smells. Additional details are available here.

Experiments have shown that the presence of the COVID-19 virus near nerve cells in the nose causes an influx of immune cells called microglia and T cells. These sense and help fight the infection.

These cells then release proteins called cytokines that changed the genetic activity of olfactory nerve cells. The genetic activity is changed even though the virus can’t infect them.

Usually the immune cell activity clears out quickly. Theories suggest that in the brain’s immune signaling persists in a way that reduces the activity of genes needed for the building of olfactory receptors.

These findings provide the first explanation of loss of smell in COVID-19 patients.


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There is more to learn about this

COVID-19 is different in that you can lose your sense of smell without getting a stuffy nose.

Usually,  the smell loss lasts only a few weeks, but for more than 12 percent of people with COVID-19, olfactory dysfunction persists.  It can carry on in the form of ongoing reduction in the ability to smell (hyposmia) or changes in how a person perceives the same smell (parosmia).

Experts wanted to learn more about the loss of smell from COVID-19. This led then to explore COVID-19 in golden hamsters in comparison to olfactory tissue taken from 23 human autopsies.

Hamsters are a good model for comparison. This is because they are both mammals.

“Experiments confirmed that SARS-CoV-2 infection, and the immune reaction to it, decreases the ability of DNA chains in chromosomes that influence the formation of olfactory receptor building to be open and active, and to loop around to activate gene expression.”

Next, the research team is working with hamsters with long COVID to see if steroids can restore damaging immune reactions and protect “nuclear architecture.”


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