According to research from experts in the United States, the loss of smell and taste when infected with Covid-19 is not directly caused by the virus but rather by inflammation.
The loss of smell and taste has become a prominent symptom in individuals infected with Covid-19 since the beginning of the pandemic and has even persisted as a long-term consequence. Researchers are still investigating the reasons behind this phenomenon.
A post-mortem study published in JAMA Neurology on April 13 reveals that the loss of smell and taste associated with Covid-19 is not caused by the virus itself.
Loss of smell and taste has become a prominent symptom in individuals infected with Covid-19.
The study analyzed data from the nasal mucosa, nerve fibers, and brains of 23 individuals who died from Covid-19. This result is considered the most detailed assessment of the impact of SARS-CoV-2 on the human olfactory and gustatory systems.
Scientists at Johns Hopkins University concluded that inflammation not caused by the virus is the reason for the loss of smell and taste during and after Covid-19 infection. This suggests that anti-inflammatory treatments could prevent severe or long-term damage to these senses.
This finding is based on a combination of various data regarding the effects of SARS-CoV-2 on human olfaction. Some previous data indicated that the virus might infect the nerve fibers that carry scent signals to the brain, known as olfactory neurons. Thus, the loss of these senses could be due to direct infection. However, in this new study, the authors found that the virus was not present in these nerve cells.
The 23 deceased individuals included 9 who experienced complete or partial loss of smell and taste. This was observed when examining the olfactory neurons in the nasal mucosa, blood vessels, and the number of olfactory axons in each patient. The authors also assessed damage to the olfactory region of the brain, where scent signals are processed, and checked for the presence of SARS-CoV-2.
They compared the study results with 14 individuals who died from other causes and did not have Covid-19 or any loss of smell or taste.
Compared to the control group and individuals without changes in smell or taste, Covid-19 patients who lost their sense of smell and taste showed more damage in the nasal mucosa and blood vessels. Meanwhile, the number of olfactory axons was significantly lower.
However, this olfactory tissue damage was not related to the severity of the disease. Additionally, only 3 out of the 23 patients had genetic material from SARS-CoV-2 in their olfactory tissues. Among these 3 individuals, only one reported a loss of smell, while the other two did not experience any loss of taste. These results indicate that “olfactory pathology is not directly caused by the virus.”
According to the authors, their findings suggest that SARS-CoV-2 infection in the olfactory epithelium leads to inflammation. Consequently, inflammatory nodules damage the nerve cells, reducing the number of axons that send signals to the brain, ultimately resulting in dysfunction of the sense of smell.
Olfactory dysfunction can be severe enough to cause long-term loss of smell and taste, even leading to permanent damage. These results also provide new hope for treating long Covid-19 symptoms. If the cause of the loss of smell and taste is due to inflammation rather than direct viral damage, anti-inflammatory agents could be used for treatment.
