New research led by scientists at Harvard University School of Medicine explains one of the many mysteries of COVID-19: why people infected with the virus temporarily lose their sense of smell.
Loss of smell has been the most common neurological symptom of the virus. The study’s lead author, Dr. Sandeep Robert Datta, said his findings about why that happens were a surprise and could lead to eventual treatments for a variety of neurological disorders caused by the virus.
Harvard neuroscientists looked closely at a specialized type of sensory neurons in the nose that detect and transmit odors to the brain.
“Our intuition, and I think many other people’s intuition, would be that the virus would attack these sensory neurons and damage or kill these neurons, and that’s how we lose our sense of smell,” said Datta, an associate professor of neurobiology. at the Blavatnik Institute at Harvard Medical School. The Datta-led study was published Friday in the journal Science Advances.
“But looking at our data, we had a big surprise,” he said. “What appears to be that the virus is not actually capable of attacking neurons that live in the nose.”
Instead, scientists discovered that two other types of cells that support those neurons are under attack. Those cells can regenerate more quickly.
“And therefore we believe that overall this is good news and suggests that people who lose their sense of smell are, for the most part, going to regain their sense of smell,” Datta said.
That’s what doctors have seen as the epidemic has progressed: Most patients regain their sense of smell within several weeks.
“We finally have clues that lead us to understand how the virus might attack your sense of smell,” Datta said, “leading to theories about how it might attack your overall neurological systems.”
In addition to loss of smell, the virus has caused a number of other neurological symptoms, including impaired consciousness, difficulty concentrating, sensory motor deficits, and strokes. Datta said he is hopeful that this new understanding of what cells the virus attacks in the nose could be helpful in understanding those other symptoms.
“I think that points the way to important treatment strategies, both for people who have lost their sense of smell and for people suffering from various neurological consequences of COVID,” he said.
The study also examined a part of the brain called the olfactory bulb that is responsible for obtaining information from the nose, and found that neurons are also not infected with the coronavirus.
“It is possible, even given our research, that the virus infects some types of neurons,” Datta acknowledged. “At least for now, our best guess is that it primarily targets vascular cells that help fuel the brain. I think that changes our strategies on how we might be able to control the virus and manage the neurological symptoms associated with COVID in the future.” ”
COVID-19 patients have also lost their sense of taste, and Datta said that’s more than just a side effect of losing the ability to smell.
“It is clear from the data available now that the coronavirus also independently attacks its sense of taste,” he said, adding that the same types of supporting cells can also be attacked by taste.
“In a preliminary analysis by colleagues of mine, it appears that the virus does not attack neurons that transmit taste information,” he said.
More research is needed to verify the document’s conclusion, Datta said, and to understand how the virus attacks the brain. She said that lack of access to autopsy studies has hampered that type of study.
And although most patients who survive COVID-19 regain their sense of smell, Datta said some do not.
“And while I think for most people, that doesn’t seem like a big problem, we know from other people who have lost their sense of smell that it is a big risk factor for depression and other kinds of psychological changes.” he said. “Because we as humans, even though we don’t think much about our sense of smell, we are deeply emotionally dependent on our sense of smell for our daily well-being.”
