Study of nose and throat reveals why people with COVID-19 may lose their sense of smell
Researchers studying tissue removed from patients’ noses during surgery believe they may have discovered the reason why so many people with COVID-19 lose their sense of smell, even when they have no other symptoms.
In their experiments they found extremely high levels of angiotensin converting enzyme II (ACE-2) only in the area of the nose responsible for smelling. This Enzyme is thought to be the ‘entry point’ that allows coronavirus to get into the cells of the body and cause an infection.
The researchers say their findings, published today (Wednesday) in the European Respiratory Journal , offer clues as to why COVID-19 is so infectious and suggest that targeting this part of the body could potentially offer more effective treatments.
The study was by Professor Andrew P. Lane, director of the division of rhinology and skull base surgery, and Dr Mengfei Chen, research associate, and colleagues from Johns Hopkins University School of Medicine, Baltimore, USA.
Professor Lane said: “I specialise in nasal and sinus problems, so the loss of the sense of smell in COVID-19 is of particular clinical interest to me. While other respiratory viruses generally cause loss of the sense of smell through obstruction of airflow due to swelling of the nasal passages, this virus sometimes causes loss of smell in the absence of other nasal symptoms.”
The team used tissue samples from the back of the nose of 23 patients, removed during endoscopic surgical procedures for conditions such as tumours or chronic rhinosinusitis, an inflammatory disease of the nose and sinus. They also studied biopsies from the trachea (windpipe) of seven patients. None of the patients had been diagnosed with coronavirus.
In the lab, the researchers used fluorescent dyes on the tissue samples to detect and visualise the presence of ACE2 under a microscope and compare levels of ACE2 in different cell types and parts of the nose and upper airway. 
They found by far the most ACE2 on the lining cells of the olfactory epithelium, the area at the back of the nose where the body detects smells. The levels of ACE2 in these cells was between 200 and 700 times higher than other tissue in the nose and trachea….
Image Credit: Amanda Scott/Envato
Thanks to Heinz V. Hoenen. Follow him on twitter: @HeinzVHoenen