Why COVID-19 Patients Lose Their Sense of Smell
Hello all! We have had fantastic feedback on all of the Sci4Teens winning entries that we have published so far- we hope you are enjoying reading some of the amazing work young people globally are doing. Cellfie are so excited to be a partner of Sci4Teens as the competition showcases young people's commitment to STEM and gives them a chance to explore areas which interest them and attempt high quality research skills. Today we present Emma Wasserman's article which came 2nd for the "Impacts of Covid-19" category. Well done, Emma!
Abstract:
The SARS-CoV-2 virus (COVID-19) has caused one of the largest global pandemics in human history. Its highly contagious nature along with the lack of proper response to its outbreak has caused the infection of around 109 million, and the death of approximately 2.4 million people worldwide. Along with common symptoms of shortness of breath, fever, and general fatigue, many people diagnosed with COVID-19 also experience a sudden loss of smell, known as “hyposmia” when only partial, and “anosmia” when complete. This loss of smell can be one of the earliest indicators of infection, and is most often temporary in COVID-19 patients. Anosmia and hyposmia are common post-viral symptoms, even in people with cases of merely a common cold. However the way in which they affect COVID-19 patients add to the factors that make SARS-CoV-2 so unique.
How we smell:
Smelling, and the ability to detect specific scents, is one that is often taken for granted and deemed “unimportant” in today’s society. (A 2011 McCann Worldgroup study actually showed that a majority of the young people they interviewed claimed “that smell was less valuable to them than their technological devices.”) Yet most people fail to realize how complex the process of sniffing is, and what really goes on when you take a deep inhale near an oven filled with cookies, or accidently catch a whiff of the pig pen at the zoo. There are two ways that we “smell”; the first is probably the way most people are familiar with, which is through our nostrils, and the second is actually through the roof of our throat, which leads up to our nose. Once microscopic particles in the air travel through either of these pathways and reach a patch of tissue high inside the nose where olfactory sensory neurons are, the particles stimulate the receptors in these cells. Whatever receptor (or combination of receptors) is triggered in the olfactory neurons, then signals our brain as to what scent is being detected. Without our sense of smell, not only would it be difficult to distinguish our favorite foods from one another, but lives could be put in danger if, for instance, a gas leak goes unnoticed, or some unknowingly expired food is consumed.
Why COVID-19 affects how we smell:
It’s widely known that the coronavirus primarily impacts a person by causing damage to the respiratory system by attacking their lungs, so why is it that a temporary lost sense of smell comes with it? Dr. Robert Datta of Harvard Medical School conducted research with his colleagues to answer this very question, and settle on the verdict that coronavirus particles don’t actually impact the olfactory sensory neurons, but instead cause a loss of function in the supporting cells surrounding them, which in turn inhibits the sensory neurons. The team reached this conclusion by focusing on ACE2 and TMPRSS2, two genes that SARS-CoV-2 uses to enter and infect human cells. These genes were apparently found in the olfactory epithelium - “a specialized tissue in the roof of the nasal cavity responsible for odor detection, that houses olfactory sensory neurons and a variety of supporting cells.” - at similar levels to cells in the lower respiratory tract, which is the part of the body the virus most commonly attacks. Because of this, they are extremely susceptible to contracting the virus and acquiring the damage that comes with that. However, neither ACE2 or TMPRSS2 were found in the olfactory sensory neurons themselves, which means that they are still able to work and regenerate, but are just weakened due to their collapsing support system. This is why hyposmia and anosmia, when found in COVID-19 patients, is often temporary.
Conclusion:
The SARS-CoV-2 virus causes a lack of smelling ability in infected patients due to its negative effect on the cells surrounding those responsible for detecting scent. Because it does not directly impact olfactory sensory neurons, patients are often able to recover from the hyposmia or anosmia they develop while fighting the virus, and recover their sense of smell.
References:
“How COVID-19 Can Impact Your Sense of Smell.” Penn Medicine,
www.pennmedicine.org/updates/blogs/health-and-wellness/2020/june/covid-and-smell.
Jarvis, Brooke. “What Can Covid-19 Teach Us About the Mysteries of Smell?” The New York Times, The New York Times, 28 Jan. 2021,
www.nytimes.com/2021/01/28/magazine/covid-smell-science.html.
Jiang, Kevin. “How COVID-19 Causes Loss of Smell.” How COVID-19 Causes Loss of Smell | Harvard Medical School, 24 July 2020,
hms.harvard.edu/news/how-covid-19-causes-loss-smell#:~:text=Together%2C%20these% 20data%20suggest%20that,sensory%20neurons%2C%20the%20authors%20said.
Kay, Leslie. “Why COVID-19 Makes People Lose Their Sense of Smell.” Scientific American, Scientific American, 13 June 2020,
www.scientificamerican.com/article/why-covid-19-makes-people-lose-their-sense-of-smell 1/.
“Smell Disorders.” National Institute of Deafness and Other Communication Disorders, U.S. Department of Health and Human Services, 14 Dec. 2020,
www.nidcd.nih.gov/health/smell-disorders#:~:text=Your%20ability%20to%20smell%20co mes,neuron%20has%20one%20odor%20receptor.