Abstract
Human-to-human transmission of coronavirus (SARS-CoV-2) - COVID-19 (corona virus disease 2019) - is characterized by a pandemic exponential rate and the patients with mild to moderate infection have odor and taste problems that represent a new atypical disease. A new viral syndrome of acute anosmia or "new loss of taste or smell" without rhinitis and nasal obstruction or rhinorrhea has been placed on the list of symptoms that may occur 2 to 14 days after exposure to the COVID-19 virus. Two months after declaring the COVID-19 pandemic in May 2020, the World Health Organization (WHO) has recognized changes in the perception of smell and taste as symptoms of this disease. The described cardinal symptoms are more common in the population of young patients and able-bodied people which facilitates the spread of disease. Significantly higher prevalence of patients with COVID-19 who have lost their taste and smell is treated at home (rare hospitalization), lung damage is rare, as well as oxygen therapy with mild lymphopenia. Different scenarios of SARS-CoV-2 viral infection can be assumed: it is probable that the virus does not enter directly into olfactory sensory neurons (they do not have ACE2 and TMPRSS2 receptors), but it is localized to vascular pericytes and causes inflammatory processes and vasculopathies. On the other hand, direct infection of non-neuronal cells which contain said receptors is possible. Those are specific cell types in the olfactory epithelium such as sustentacular, horizontal basal cells, as well as Bowman's glands, which leads to massive degeneration and loss of olfactory neurons. The sense of taste is a complex sensation that is the result of the interaction of smell, taste, temperature and texture of food. The virus damages cranial nerves, epithelial receptors and blood vessels leading to taste damage (ageusia or dysgeusia). A multidisciplinary approach with epidemiological, clinical and basic research is needed to elucidate the mechanism of sensorineural odor and taste loss caused by coronavirus.
Highlights
A multidisciplinary approach with epidemiological, clinical and basic research is needed to elucidate the mechanism of sensorineural odor and taste loss caused by coronavirus
SARS-CoV-2 is transmitted from person to person through respiratory droplets, which leads to respiratory tract infection that can progress to severe pneumonia, multiple infections of vital organs and fatal outcomes
The syndromes described in the current SARS-CoV-2 epidemic (COVID-19) are asymptomatic, mild, moderate and severe or disease, such as bilateral interstitial pneumonia [1,2,3,4]
Summary
Receptor behavior is improved: one neuron - one olfactory receptor that acts on the principle of “key and lock”. Each olfactory cell carries only one type of receptor protein for a particular substance (smell) or “lock”, while the smell floats in the air, fits into the “lock” and activates the cell. Smell sensation creates an electrical receptor potential in response to the olfactory nerves: an odor molecule binds to a receptor belonging to receptors associated with the G protein/cAMP cascade, located in the cilia of bipolar neurons in the olfactory mucosa. Olfactory receptors open non-specific cation channels permeable to Ca2+ and induce receptor potential. This is how odor receptors play a crucial role in recognizing thousands of odor molecules. Odor receptors have a unique ability to regenerate from stem cells when they are injured or old [45,47]
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