Context:

• Multiple reports have surfaced, primarily from Europe and the United States, from physicians and ear, nose and throat specialists, of COVID-19 patients complaining of an inability to smell — or anosmia. However, it is not clear whether neurons in the brain that are responsible for recognising various odours are damaged, or whether other cells may be involved.

COVID-19: Not Directly:

• A research suggests that it is not neurons but a class of cells in the upper regions of the nasal cavity that may be involved. These are called sustentacular cells and horizontal basal cells.
• The sustentacular cells and horizontal basal cells:
• Crucially, both are not directly involved in helping us smell, but nourish and support the cells that help us do.
• So the virus may be inflicting an indirect attack on the olfactory sensory cells.
• Another research points out the presence of a key enzyme — called ACE 2 (Angiotensin Converting Enzyme) — in these olfactory cells.
• The coronavirus has spike proteins that bind to ACE 2 receptors on human cells and the enzyme’s presence is a proxy to reveal the signature of the virus in the body’s cells.

Anosmia:

• Anosmia is the partial or complete loss of the sense of smell. This loss may be temporary or permanent.
• It is caused by a swelling or blockage in the nose that prevents odors from getting to the top of the nose.
• Respiratory viral infection is a common cause of loss of smell. The sense of smell usually returns when the infection is over.

Other Main Causes of Anosmia:

• Irritation to the mucous membranes lining the nose.
• Blockage of the nasal passages.
• Brain or nerve damage.
• Complications: People with anosmia may not be able to fully taste foods and may lose interest in eating.
• This can lead to weight loss or malnutrition.

Ageusia:

• Ageusia is a condition that is characterized by a complete loss of taste function of the tongue.
• People who have a reduced ability to taste are said to have Hypogeusia.

Common Causes:

• Aging
• Nasal airway problems.
• Upper airway infection, such as sinus infection, tonsillitis, or sore throat.