Scientists have discovered why coronavirus causes some patients to lose their sense of smell.
Studies suggest the “devastating” symptom better predicts the disease than other well-known symptoms such as a fever or cough.
But the actual cause for loss of smell in Covid-19 patients has been unclear – until now.
Researchers at Harvard Medical School in the United States have identified which cell types used for smelling are most vulnerable to infection by SARS-CoV-2, the virus that causes Covid-19.
They were surprised to discover sensory neurons, which detect and transmit the sense of smell to the brain, are not vulnerable to the disease.
Their study instead found it attacks the cells supporting the olfactory sensory neurons.
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Dr Sandeep Robert Datta, associate professor of neurobiology at Harvard Medical School and co-author of the study, said this was a positive finding because it suggests most cases of Covid-19 are unlikely to cause a permanent loss of smell.
He said: “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.
“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.”
But, he added: “We need more data and a better understanding of the underlying mechanisms to confirm this conclusion.”
The majority of Covid-19 patients experience some level of anosmia, but most often it is temporary.
The research team hope the study results will help accelerate efforts to better understand smell loss in Covid-1 patients, which could lead to treatments for anosmia and the development of improved smell-based diagnostics for the disease.
Dr Datta said: “Anosmia seems like a curious phenomenon, but it can be devastating for the small fraction of people in whom it’s persistent.
“It can have serious psychological consequences and could be a major public health problem if we have a growing population with permanent loss of smell.”
The study was published in the peer-reviewed journal Science Advances.