Scientists discover why coronavirus patients lose sense of smell – and offer hope to those who haven’t got it back yet

THE KEY symptoms of coronavirus are now widely known as a new and persistent cough, a high temperature and a loss of taste and smell.

But many have been left mystified as to why the respiratory infection would prevent someone from being able to smell.

Now, scientists say they have the answer – and it’s promising news if you’re someone who still hasn’t had their sense of smell back yet.

A team of experts at Harvard Medical School have identified the cell group which is most vulnerable to Covid-19.

They found the neurons that detect and transmit the sense of smell to the brain are not part of the vulnerable cells.

Researchers did however discover that the ACE 2 receptor protein that Covid uses to enter human cells is found in cells that provide metabolic and structural support.

Non neural cells are found in the central nervous system.

The experts said that their research suggests that it is these cells that are responsible for anosmia (loss of taste and smell) in Covid-19 patients.

Writing in Science Advances senior study author Sandeep Robert Datta 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.”

They say that it means most people who develop anosmia due to Covid-19 will be able to regain their senses.

The findings come after an alternative study found that one in ten coronavirus patients who lose their sense of taste and smell will not get it back.

Researchers compiled their data from Italian patients and found that 49 per cent had fully regained their sense of smell or taste after recovering from the virus.

This is while just 40 per cent reported improvements and 10 per cent said their symptoms had worsened.

Meanwhile analysis of electronic health records found that coronavirus patients are 27 times more likely to have a loss of smell but are 2.2 to 2.6 times more likely to have other respiratory difficulties compared to non Covid patients.

Datta and the team at Harvard looked to how a loss of sense and smell is altered in patients with Covid-19.

They found that cells that wrapped around sensory neurons (setentacular cells) provided metabolic support.

While basal cells helped regenerate after they were damaged.

The olfactory epithelium is found in the nasal cavity and researchers found that these expressed higher levels of ACE 2 protein compared with resting stem cells.

The authors said that anosmia in Covid-19 patients could arise from a loss of supporting function in the olfactory epithelium which indirectly causes changes to olfactory sensory neurons.

Datta added: “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 team added that the research will offer hope to those who have not yet got their senses back as they claim it does not cause permanent damage.