Loss of Sense of Smell Caused by COVID-19

Aditi Kaveti ‘23

Figure 1: Coronavirus

The coronavirus pandemic has changed our lifestyles as we knew it. As we find ways to stay safe during the pandemic, research continues to bring us new information about COVID-19. One of the earliest and most commonly reported indicators of COVID-19 is the temporary loss of smell, or anosmia. Olfactory cells are the body’s smell nerve cells that are stimulated by the odors around us. While other symptoms include fever and cough, anosmia better predicts COVID-19 despite its previously unclear underlying mechanism. Normally, sensory neurons that detect and transmit the sense of smell to the brain are not a vulnerable cell type. SARS-CoV-2 uses the ACE2 receptor protein to enter human cells, but previous research has found that olfactory sensory neurons do not express the gene that encodes ACE2.

An international team of researchers led by neuroscientists at Harvard Medical School identified the olfactory cell types most vulnerable to the virus that causes COVID-19, SARS-CoV-2. Their findings suggest that the anosmia caused by COVID-19 may be due to the infection of nonneural cell types and affecting the function of supporting cells. This type of infection suggests that the SARS-CoV-2 infection is unlikely to permanently damage olfactory neural circuits, and that the majority of patients will experience only temporary anosmia. 

The team analyzed existing single-cell sequencing datasets that catalogued the genes expressed by hundreds of thousands of individual cells in the upper nasal cavities of humans, mice, and nonhuman primates. They found that ACE2 is expressed by the cells in the olfactory epithelium but is not expressed by olfactory sensory neurons. The data collected suggests that COVID-19-related anosmia could be explained by a temporary loss of function of supporting cells in the olfactory epithelium, which then indirectly causes changes to olfactory neuron sensors. Further research will involve collecting more data to gain a better understanding of the underlying mechanisms and changes in the olfactory neuron sensors that are linked to COVID-19.

Works Cited:

  1. Harvard Medical School. How COVID-19 causes smell loss: Olfactory support cells, not neurons, are vulnerable to novel coronavirus infection. ScienceDaily, (2020). http://www.sciencedaily.com/releases/2020/07/200724141027.htm
  2. Image retrieved from: https://pixabay.com/illustrations/covid-19-coronavirus-social-distance-4975604/

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