Many patients with COVID-19 report a tell-tale loss of smell and taste, which can last for weeks or even months after infection.
New research has suggested that the best way to treat the symptom is not drugs, but ‘smell training’.
The process involves sniffing at least four different odours twice a day for several months.
The researchers say that corticosteroids – a class of drug that lowers inflammation in the body – are not recommended to treat smell loss due to COVID-19.
Smell loss expert Professor Carl Philpott, from the University of East Anglia’s Norwich Medical School, said: “The huge rise in smell loss caused by COVID-19 has created an unprecedented worldwide demand for treatment.
“Around one in five people who experience smell loss as a result of COVID-19 report that their sense of smell has not returned to normal eight weeks after falling ill.
“Corticosteroids are a class of drug that lowers inflammation in the body. Doctors often prescribe them to help treat conditions such as asthma, and they have been considered as a therapeutic option for smell loss caused by COVID-19.
“But they have well-known potential side effects including fluid retention, high blood pressure, and problems with mood swings and behaviour.”
The researchers reviewed existing evidence to see whether corticosteroids could help people regain their sense of smell – or whether ‘smell training’ was more effective.
Prof Philpott said: “What we found is that there is very little evidence that corticosteroids will help with smell loss. And because they have well known potential adverse side effects, our advice is that they should not be prescribed as a treatment for post-viral smell loss.
"There might be a case for using oral corticosteroids to eliminate the possibility of another cause for smell loss actually being a confounding factor, for example chronic sinusitis – this is obviously more of a diagnostic role than as a treatment for viral smell loss.
“Luckily most people who experience smell loss as a result of COVID-19 will regain their sense of smell spontaneously. Research shows that 90% of people will have fully recovered their sense of smell after six months.
“But we do know that smell training could be helpful. This involves sniffing at least four different odours twice a day every day for several months. It has emerged as a cheap, simple and side-effect free treatment option for various causes of smell loss, including COVID-19.
“It aims to help recovery based on neuroplasticity – the brain’s ability to reorganise itself to compensate for a change or injury,” he added.
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Research earlier this year showed that coronavirus can travel into people’s brains through nerve cells in their nose.
Researchers analysed post-mortem tissue from COVID-19 victims, and were able to capture electron microscope images of coronavirus particles inside the olfactory mucosa, in the upper part of the nasal cavity.
More than one in three COVID-19 patients report neurological symptoms, including the telltale loss of smell and taste.
Other patients suffer from headaches, fatigue, dizziness, and nausea, according to the researchers at Berlin’s Charité - Universitätsmedizin Berlin.
In some patients, the disease can even result in stroke or other serious conditions.
Researchers studied tissue samples from 33 patients (average age 72) who had died at either Charité or the University Medical Center Göttingen after contracting COVID-19.
Researchers analysed samples taken from the deceased patients' olfactory mucosa and from four different brain regions.
Both the tissue samples and distinct cells were tested for SARS-CoV-2 genetic material and a 'spike protein' which is found on the surface of the virus
The olfactory mucosa revealed the highest viral load.
"These data support the notion that SARS-CoV-2 is able to use the olfactory mucosa as a port of entry into the brain," says Professor Frank Heppner,
"Once inside the olfactory mucosa, the virus appears to use neuroanatomical connections, such as the olfactory nerve, in order to reach the brain.
"It is important to emphasize, however, that the COVID-19 patients involved in this study had what would be defined as severe disease, belonging to that small group of patients in whom the disease proves fatal.
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