New COVID-19 research on the significance of smell loss suggests COVID-19 infects the brain and nervous system.

As most people are now aware, the loss of smell is one of the characteristics of having COVID-19. But what does that mean in scientific terms? Is the smell loss the same as we might experience with a bad cold or flu? And how can that help the battle against COVID, particularly if we have a second wave that coincides with a severe outbreak of flu?

Expects have discovered that smell and taste disorders associated with COVID-19 differ from those with other causes of upper respiratory tract infections.

Prof Philpott at the Norwich Medical School, University of East Anglia (UEA), known for its world-leading research in the fields of environment, health and plant science, is a member of a European research team led by the Cliniques Universitaires Saint-Luc (Belgium), Université catholique de Louvain (Belgium) in collaboration with researchers at  University of East Anglia/The Norfolk Smell and Taste Clinic at the James Paget University Hospital (UK), Aristotle University (Greece), Acibadem Taksim Hospital in Istanbul (Turkey), Biruni University (Turkey) and University Hospital of Foggia (Italy).

The team have today published a new study which they hope could help develop smell and taste tests for fast Covid-19 screening in primary care and emergency departments would differentiate between people with Covid-19 as opposed to a regular cold or flu.

Their findings show that the main difference between COVID-19 smell loss and other health issues such as flu is that COVID patients can breathe freely, do not tend to have a runny or blocked nose, and they cannot detect bitter or sweet tastes.

These findings lend weight to the theory that Covid-19 infects the brain and central nervous system.

The research team carried out smell and taste tests on 10 Covid-19 patients, 10 people with bad colds and a control group of 10 healthy people – all matched for age and sex.

Lead researcher Prof Carl Philpott, from UEA’s Norwich Medical School, said:

We know that Covid-19 behaves differently to other respiratory viruses, for example by causing the body’s immune system to over-react, known as a cytokine storm, and by affecting the nervous system.

We found that smell loss was much more profound in the Covid-19 patents. They were less able to identify smells, and they were not able to identify bitter or sweet tastes. In fact, it was this loss of true taste which seemed to be present in the Covid-19 patients compared to those with a cold.

This is very exciting because it means that smell and taste tests could be used to discriminate between Covid-19 patients and people with a regular cold or flu.

Although such tests could not replace formal diagnostic tools such as throat swabs, they could provide an alternative when conventional tests are not available or when rapid screening is needed – particularly at the level of primary care, in emergency departments or at airports.

This research also shows that there are altogether different things going on when it comes to smell and taste loss for Covid-10 patients, compared to those with a bad cold.

It has previously been suggested that the Covid-19 virus affects the central nervous system, based on the neurological signs developed by some patients. There are also similarities with SARS, which has also been reported to enter the brain, possibly via smell receptors in the nose. Our results reflect, at least to some extent, a specific involvement at the level of central nervous system in some COVID-19 patients.

It is particularly interesting that Covid-19 seems to particularly affect sweet and bitter taste receptors, because these are known to play an important role in innate immunity.

More research is needed to see whether genetic variation in people’s bitter and sweet taste receptors might predispose them to Covid-19, or conversely, whether Covid-19 infection changes how these receptors function, either directly or through a cytokine storm – the over-reaction of the body’s immune system.

‘Comparison of COVID-19 and Common Cold Chemosensory Dysfunction’ is published in the journal Rhinology on August 19, 2020.

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