Scientists Learn why the Loss of Smell is a Symptom of COVID-19

Updated: Oct 18, 2021

The loss of smell is one of the most commonly reported symptoms of COVID-19, with studies . However, up until now, scientists were unsure as to why. Recently, an international group of researchers at Harvard University discovered how and why anosmia, the temporary loss of smell, is such a commonly reported symptom of COVID-19. This study has uncovered yet another mystery of the novel virus and its findings are expected to aid in better understanding it.

Anosmia has been reported to be the main neurological symptom of the novel virus. Studies suggest that the symptom may be the best indicator of the infection in comparison to a fever and cough. This has been indicated by analyzing electronic health records and following the trends that have been observed, which show that patients who have contracted COVID-19 are 27 times more likely to experience some form of anosmia in comparison to people without the disease. This is far greater than the likeliness of someone with the virus and having a fever or a cough, which is roughly 2.2 – 2.6 times more likely than someone without the virus.

The aforementioned group of researchers at Harvard University were behind the study that recently identified why the loss of smell is such a common symptom of COVID-19. The group of researchers — led by Sandeep R. Datta, associate professor of neurobiology at Harvard Medical School — observed thousands of publicly available genetics datasets. The study was supported by grants from the National Institutes of Health and the Simons Collaboration on the Global Brain. The study was published in the peer-reviewed journal “Science Advances.”

To understand which cells are affected in the upper naval cavity by SARS-CoV-2, another term for COVID-19, the team of researchers began analyzing the genes ACE2 and TMPRSS2. ACE2 has the primary purpose of encoding the main receptor proteins that the virus uses to enter human cells. On the other hand, TMPRSS2 encodes enzymes that the virus also utilizes to gain traction and spread in human cells.

Through analysis of different datasets, it was found that both genes are expressed by cells in the olfactory epithelium, a tissue in the nasal cavity that holds olfactory sensory neurons. In the olfactory epithelium, scientists found two prominent cell types that were analyzed and suggested to be vulnerable to the infection. This finding allowed them to determine that the damage to the olfactory neural circuits is unlikely to cause permanent damage, meaning patients can recover their sense of smell.

To further study expression of SARS-CoV-2 entry genes, the neurosurgeons observed gene expression in 50,000 individual cells in the mouse olfactory bulb in different cell types of mouse olfactory epithelium. The study stated the utilization of mice was due to the fact that they “enable interrogative experiments not possible in humans.”

The senior author of the study at hand, Sandeep Robert Datta, briefly shared his findings in a statement. “Our findings indicate that the novel coronavirus changes the sense of smell in patients not by directly infecting neurons but by affecting the function of supporting cells.”

Datta added that the implication of this finding is that in most cases, COVID-19’s symptom of loss of smell is unlikely to develop permanently into persistent anosmia. Persistent anosmia is caused by damage to the olfactory neural circuits and is mainly associated with mental and social health issues such as depression and anxiety. “Anosmia seems like a curious phenomenon, but it can be devastating for the small fraction of people in whom it’s persistent,” Datta said.

The findings from this study hint to many clues associated with other neurological issues of COVID-19. For example, the authors of the study said the results from the study at hand are consistent with the hypothesis that SARS-CoV-2 does not directly infect neurons. Instead, it may interfere with brain function through the nervous system. However, this hypothesis still needs further investigation. Scientists are hopeful that by observing further, their efforts in creating a treatment of the disease will be accelerated.

Through Teen Lenses: Although scientists are still pondering many aspects of COVID-19, researchers have determined why the temporary loss of smell, or Anosmia, is one of the main neurological symptoms of the virus. Do you believe this new understanding of the novel virus will be of any use? What do you expect to come in the future in regards to research and a better understanding of the virus?

“I believe that determining loss of smell as one of the main neurological symptoms of COVID-19 could help better diagnose people with the virus. However, loss of smell is a common symptom of many other infections so I do not believe that this discovery would be of much use. In the future I expect researchers to continue to find other significant symptoms related to the virus as well as developing a working vaccine.” Sricharan Sattiraju, 15, Rising Sophomore at Thomas Jefferson High School for Science and Technology, Chantilly, Virginia
“I believe that this new knowledge of the virus will help scientists better understand the virus as they will be able to make connections with this discovery to other aspects of COVID-19. If scientists understand why one symptom of the virus occurs, through extensive research and testing, they may be able to find out why other symptoms occur. From the knowledge of symptom background along with tracings of medical history, prevention methods can be implemented to control the spread. Scientists will be able to continue further studying the virus with new and old info and hopefully find a good cure and vaccine in the future.” Anchita Shukla, 17, Rising Senior at Chantilly High School, Fairfax, VA
“I think this new understanding of COVID-19 will definitely be of use, because it gives us a very distinct symptom to look for. Most COVID symptoms could be often confused with cold or flu symptoms, and this one is definitely more unique. Finding out about anosmia can also help with creating effective treatments and better understanding how the virus affects certain genes. I expect that soon in the future an effective enough treatment to stop people with COVID from dying from it will be created and after that a vaccine will be finished that can fully end the spread of COVID-19 and protect us from the possibility of COVID resurfacing.” Megan Enochs, 15, Rising Sophomore at Thomas Jefferson High School for Science and Technology, Haymarket, Virginia