Not being able to detect the taste of food or smell the odors around us is more than a crippling situation that many Covid-19 patients experience. According to the latest meta-analysis on the subject, between 41 and 62% of them have suffered total or partial anosmia (loss of smell), often accompanied by ageusia (loss of taste). These are sometimes the first signs of Covid-19, appearing about three days before any other symptoms.
How long do patients have to deal with the diminished senses?
According to Canadian physician Johannes Frasnelli, who works at the University of Quebec, anosmia can last for more than five months. He conducted a study, the abstract of which was pre-released on February 22, 2021, among more than 800 health care workers in Canada. The full results of the study will not be presented until the 73rd Annual Meeting of the American Academy of Neurology, scheduled for mid-April 2021.
Even after 5 months, both taste and smell are not fully recovered
Johannes Frasnelli’s conclusions were based on the subjective feelings of the participants, not a clinical diagnosis of anosmia. In fact, participants filled out an online questionnaire for 5 months and rated their anosmia and ageusia during tests they performed themselves at home. They rated their sensory disturbances from 0 to 10, with 0 corresponding to a complete lack of smell or taste and 10 to a complete recovery of the senses.
Of the 813 participants, 580 lost their sense of smell. Of these 500, 51% did not recover their full olfactory capacity after 5 months, and 17% reported a persistent loss of smell. On average, they rated their sense of smell as 7 out of 10 after Covid-19, compared to 9 out of 10 before.
Also, 527 were affected by ageusia, and 38% still suffered from it 5 months later. As with smell, participants rated their sense of taste lower after Covid-19, 8 out of 10 compared to 9 out of 10 before.
“Our results show that impaired taste and smell may persist in some people with Covid-19,” says Johannes Frasnelli. This underscores the importance of monitoring infected individuals and conducting further research to determine the extent of neurological manifestations associated with Covid-19.
Reasons for loss of sense of smell still unclear
The sense of smell is the result of a subtle and complex interaction between volatile compounds, odors, and chemical receptors located on neurons in the olfactory bulb. If odors do not reach the neurons in the olfactory bulb, the brain does not perceive an odor. Olfaction disorders often occur when the nose is blocked, and this condition is then usually temporary.
But in the case of Covid 19 patients, the story is a little different as they do not suffer from nasal congestion. Italian neurologists proposed two mechanisms of pathogenesis in a recent paper published in Neuroscience Letters. In both cases, SARS-Cov-2 infection and the resulting inflammation alter the cells of the olfactory bulb. The first hypothesis is that coronavirus infection triggers inflammation of the cells of the olfactory epithelium. The perception of odors is then disturbed. In the second hypothesis, it is the cells located beyond the epithelial barrier that become infected or suffer the effects of the damaging inflammation.
A final hypothesis is that the neuroinvasive ability of SARS-Cov-2 could damage neurons. As a result, anosmia and ageusia could then be a consequence of neurological damage.
Have you lost your sense of smell or taste after catching Covid-19? How long did it take you to get your senses back? please share with our readers your experience in the comments area below!