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Woman smells herbs (symbolic image): Some people cannot smell properly even if the corona virus can no longer be detected
Photo: Guido Mieth / Getty Images
Suddenly everything just tastes like cardboard: people who have been infected with the corona virus keep reporting changes in their sense of smell and taste.
The loss of smell is now considered a typical symptom of Covid 19 disease and for some it lasts weeks or even months after infection.
A US research team has now found the possible cause of the ongoing loss of smell.
Accordingly, it is not the virus itself that damages the cells in the nose that are responsible for smelling, but rather your own immune system.
The researchers had examined the olfactory mucosa of those affected and discovered inflammatory processes there that persisted even long after the virus was no longer detectable.
"It hasn't been shown before"
"This thorough study provides evidence that persistent olfactory disorders are associated with inflammation of the olfactory mucosa," says ENT specialist Thomas Hummel from the University Hospital Dresden, who was not involved in the work.
"This has not been shown before." Peter Berlit, Secretary General of the German Society for Neurology (DGN), also speaks of a "very valuable finding".
Olfactory disorders are among the most common symptoms of Covid 19 disease, writes the team of authors led by Bradley Goldstein from Duke University in Durham in the journal Science Translational Medicine.
It is known that the coronavirus can directly affect the olfactory mucosa.
This three to five square centimeter small area lies deep in the nasal cavity in the upper nasal passage on both sides of the nasal septum and contains about ten million olfactory cells as well as supporting and stem cells.
Previous studies - including those by the Max Planck Institute for Neurogenetics in Frankfurt - had shown that the coronavirus in the mucous membrane does not infect the actual olfactory cells, but the neighboring supporting cells that supply the olfactory cells with nutrients.
In most patients with Covid-related loss of smell, the supporting cells apparently recover, and the loss of smell is only temporary.
Virus goes, inflammation stays
So far, however, it has been unclear what happens to those people in whom the olfactory disorders last longer - often several months, sometimes even years.
To answer the question, the team analyzed mucosal samples from 24 people, nine of them with prolonged loss of smell after Covid disease.
During the investigation, the researchers came across, among other things, T cells that are associated with inflammatory reactions.
Such inflammatory processes continued even if the actual infection was a long time ago.
In addition, the tissue contained noticeably few olfactory cells – their number may have fallen as a result of the ongoing inflammatory reaction.
However, the researchers admit that their conclusions are based on only a small number of samples.
The Dresden ENT doctor Hummel also criticizes this.
“I would have liked a larger number of cases.” This would also have made it possible to check whether age played a role.
According to Hummel, olfactory disorders tend to last longer in older people.
DGN Secretary General Berlit nevertheless considers the conclusions of the study to be plausible.
»You can easily conclude that from the data.«
Steroids straight up your nose
The study also provides indications of possible treatment options.
Accordingly, immune cells that promote inflammation could be inhibited.
The team of authors of the current study writes that appropriate medication can be applied specifically to the olfactory mucosa via the nose.
According to ENT doctor Hummel, anti-inflammatory drugs such as steroids or platelet-rich plasma can be used to improve the olfactory disorders.
So far, the success rate of such therapies is modest, but they may be suitable for certain patients.
Berlit refers to a study from the Netherlands recently published in the journal "BMC Medicine".
Accordingly, tablets with the cortisone preparation prednisolone brought no improvement in people who had had olfactory disorders for more than four weeks.
In view of the new findings, Berlit thinks it makes sense to now examine the direct application of cortisone to the olfactory mucosa.
Loss of smell usually lasts a year at most
In general, the neurologist emphasizes, the chance of smelling returning within a year is very high.
So far, however, there is no drug therapy with proven effectiveness, but regular olfactory training can help.
In the summer of 2021, French researchers published figures in the journal Jama Open Network on how long olfactory disorders can last.
According to this, around 84 percent of the 51 participants affected by smell loss had their sense of smell completely back after four months.
By the end of the study, 12 months later, 96 percent of the subjects had regained their sense of smell.
koe/dpa