Scientific American February 2021 pp60-63|Public Health| “How Covid Scrambles The Senses” “Explanations begin to arise at the molecular level for this vexing but commonplace phenomenon” By Stephani Sutherland
Image from "New-onset anosmia and ageusia in adult patients diagnosed with Sars-CoV2 infection" by A. Patel et al. June 02,2020 Clinical Microbiology and Infection
Read the full Scientific American article for more detail
Summary of the Article
“An estimated 80 percent of people with COVID-19 have smell disturbances [anosmia (loss of smell)], and many also have dysgeusia or ageusia (a disruption or loss of taste, respectively) or changes in chemesthesis (the ability to sense chemical irritants such as hot chillies).”
It is well understood that COVID-19 enters cells by coupling some of its viral surface proteins with compatible counterparts on receptive cells. These counterparts are known as receptors and specifically ACE2 receptors. To the relief of the experts, research has now demonstrated that ACE2 receptors are not on nasal nerve cells that actually reach into the brain. Direct transmission into the brain from the nose would have had potentially more dire long-term consequences. Currently the evidence suggests that cells that support neuron nutrition and function are infected and ultimately after infection these cells may peal away much like sunburnt skin only to be replaced in time. Without the normal supporting tissue nerve-cells for sensing smell are impaired. Taste sensing maybe impacted in a similar way.
Most patients recovery quickly from temporarily losing these senses while the effect lingers in others and some patients get mixed signals, called parosmia, where normal smells are replaced, as examples, with that taste of “ice cubes and cardboard” or “window cleaner”. The explanation for parosmia is complex but “may occur when newly grown stem cells…[that eventually will be]…developing into neurons [nerve cells]…” connect temporarily to the wrong sensing location in the “olfactory bulb” in the brain results in “erratic smell”. Treatments are being explored.
Carol Yan (UCSD Rhinologist) notes that “anosmia poses a real health risk. ‘It actually increases mortality. If you can’t smell and taste food, it can predispose you to harm, like rotten food or a gas leak…It can also cause social withdrawal or nutritional deficient.’”