Harvard Scientists Find Link Between Coronavirus and Loss of Smell

A team of Harvard scientists — led by Harvard Medical School associate professor Sandeep R. Datta — found that certain cells in the nose express genes that facilitate COVID-19 infection.

The study’s preliminary findings — published March 28 on bioRxiv, an archive of life sciences preprint manuscripts that have not been peer-reviewed — may explain why some coronavirus patients reporting a less acute sense of smell.

Datta said his research was motivated by growing anecdotal evidence of patients losing their ability to smell upon developing COVID-19 in the press and in formal medical reports.

“There seems to be a strong association between the development of disturbances in smell and getting COVID-19,” Datta said. “It seems like this may be one of the hallmarks of the disease.”

Datta said he and his collaborators collected publicly available genetics datasets to better understand how COVID-19 potentially infects cells in the olfactory system and disrupts its function.

The researchers focused on genes expressed by cell types comprising the olfactory epithelium, which Datta described as “the part of your nose that is responsible for detecting the smells and sending the information to your brain.”

There are two proteins known to be receptors for the coronavirus, according to Datta. Cells expressing both molecules may be “uniquely susceptible” to COVID-19 infection.

Datta said the group expected to find that neurons responsible for detecting odors would be most susceptible to infection. Instead, they “got a surprise” and discovered it was actually the cells supporting the sensory neurons that expressed the vulnerable genes.

“That’s interesting because it might provide some potential mechanisms for how the coronavirus might actually cause a change in your sense of smell,” Datta said. “I think, at least at first pass, those mechanisms are not the ones we would have naively expected.”

Major medical societies have publicly stated that loss of smell can serve as a powerful diagnostic of COVID-19 infection.

The American Academy of Otolaryngology — the study of the ears, nose, and throat — proposed that anosmia and dysgeusia, or the sudden and unexplained total or partial loss of smell and taste, “be added to the list of screening tools for possible COVID-19 infection,” according to a statement published on the group’s website on March 22.

In the absence of other pre-existing respiratory illnesses, disturbances of smell and taste “should alert physicians to the possibility of COVID-19 infection and warrant serious consideration for self-isolation and testing of these individuals,” the group wrote.

Though Datta said extensive clinical validation is required to confirm the findings, existing medical records indicate that loss of smell seems to happen “very rapidly.”

“It’s a little bit like a switch being flipped, where one day you smell and the next day, you don't,” Datta said.

He added that while physicians and researchers have found evidence that loss of smell may precede development of COVID-19 symptoms, patients with pre-existing loss of smell due to genetic conditions or trauma should not worry.

“There are certainly genetic conditions that can cause you to lose your sense of smell or to be more without a sense of smell,” Datta said. “None of those puts you at increased risk of getting coronavirus.”

—Staff writer Virginia L. Ma can be reached at virginia.ma@thecrimson.com.