COVID-19 and a loss of smell: Why the virus may hinder this sense

(NBC News) - A study published Tuesday sheds light on one of the more curious symptoms of COVID-19: the loss of smell.

The coronavirus infects cells by binding to a receptor found on their outer surface, called ACE2. Cells in the nose that help us detect smells are particularly rich in this receptor, according to the research released in the European Respiratory Journal — and that could make them a clear target for the virus.

In the study, Johns Hopkins University researchers examined tissue samples from the noses of 23 patients. The samples had been obtained during medical procedures for conditions unrelated to COVID-19, such as tumors or chronic rhinosinusitis, an inflammatory disease of the nose. None of the patients in the study had been diagnosed with the coronavirus. The researchers also took samples from the trachea, or windpipe.

The samples were then taken to a lab where fluorescent dyes were used to show where the ACE2 receptors were located.

The researchers found the highest concentration of ACE2 receptors in the cells lining the olfactory epithelium, the area of the nose that detects smells. In this region, levels of ACE2 receptors were between 200 and 700 times higher than levels seen in other parts of the nose and trachea.

Further research is needed to see if the coronavirus is, in fact, binding to the receptors in this part of the nose.