Lost and Found: The Sense of Smell and Taste in Covid-19 Patients

Latest research suggests that SARS-2 coronavirus infects the outer layering of tissues in the upper respiratory organs leading to the loss of smell and taste.

However, the virus does not cause permanent damage to the infected tissues which explains why patients regain these senses within one month of falling sick.

“Looking at the nasal tissues we found that the virus was infecting the olfactory epithelium which is involved in the smell,” John Nicholls, clinical professor in pathology, said in an interview last week.

Nicholls and his team at Hong Kong University conducted experiments on hampsters exposed to the virus to study how COVID-19 affects various organs of the body.

Olfactory epithelium are tissues which form the outer lining inside the nasal cavities. And these cells are part of the sensory system and provide the sense of smell to humans and animals.

Loss of smell and taste are two recurring symptoms in patients infected by the novel coronavirus. Some countries have used these symptoms as diagnostic criterion for early detection and isolation of suspected carriers.

Others like Britain have had to update their quarantine guidelines to recommend self-isolation for people experiencing anosmia -- loss or change of the sense of smell.

But the good news from the Hong Kong University study, Prof Nicholls says is that during the infection “the nerve itself is not damaged but it is just the cells which sense the smell. It will take a while for the cell to grow back once they are damaged but they seem to regrow themselves”.

A study published by the University of California in April had indicated the disease is more severe in patients not experiencing anosmia.

Only 27 percent of hospitalised patients showed loss of smell and taste as compared to 67 percent of those not hospitalised and showing milder clinical symptoms.

“So severe disease is not normally associated with loss of smell and taste and mild disease tends to be associated with the loss of these two functions.” Nicholls explains.

Loss of smell and taste does not necessarily indicate exposure to COVID-19.

Anosmia is a symptom associated with many other diseases, including common flu which continues to claim more than 2,50,000 lives world over every year.

However, the COVID-19 virus is considerably more contagious than the common influenza and has a relatively higher mortality rate.