The research team led by neuroscientists at Harvard Medical School (HMS) found that non-neuronal cell types may be responsible for loss of smell in coronavirus patients. Their findings were recently published in Science Advances.
“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,” said Sandeep Robert Datta, senior study author and associate professor of neurobiology in the Blavatnik Institute at HMS, in a university news release.
This finding implies that infection is unlikely to cause lasting damage and persistent loss of smell.
“I think it’s good news because once the infection clears, olfactory neurons don’t appear to need to be replaced or rebuilt from scratch,” Datta said. “But we need more data and a better understanding of the underlying mechanisms to confirm this conclusion.”
A separate, unrelated study found that nearly 90 percent of a given subset of coronavirus patients saw improvement in smell over four weeks. Researchers evaluated 202 mildly symptomatic adults at Treviso Regional Hospital in Italy. At four weeks, 89 percent of patients who reported a sudden onset of altered sense of smell or taste saw a complete resolution or improvement of the symptoms.
According to the Harvard researchers, other viral infections (including coronaviruses) are known to have months-long recovery times for smell. These infections are known to inflict direct damage to olfactory sensory neurons. In these viruses, inflammatory responses can cause changes in odor perception, though some cases of COVID-19 related anosmia have happened without nasal inflammation.