A new study shows that the main entry route for the virus is through the nose. This is a good reason to use the mask correctly.
Olfactory cells are the main entry route for SARS-CoV-2, which is the conclusion of a study by the team of Professor Andrew Lane and Dr. Mengfei Chen of the Johns Hopkins University School of Medicine in Baltimore, and published in the European Respiratory Journal. Scientists have discovered that olfactory cells are extremely sensitive to the virus. This would explain the partial or total loss of smell often seen in patients, but would also indicate a possible new treatment option.
So far, the key used by SARS-Cov-2 to penetrate human cells is known. It binds to a protein called ” Angiotensin-converting enzyme 2″ or ACE2, which is present in the membrane of certain cells. In humans, ACE2 is widely expressed in the lungs, kidneys, and small intestine. However, where is the main entry point of the virus? This was the question asked by researchers at John Hopkins University who followed the nasal trail because “international reports of olfactory diseases in COVID-19 patients have been reported internationally, with a reported prevalence of up to 85% in a large multicenter European survey,” the authors explain. And these reports showed that some COVID-19 patients experience loss of smell as their first or only symptom. Therefore, “loss of smell suggests the possibility of direct targeting by SARS-Cov-2”. However, “the cellular location of ACE2 protein in the olfactory epithelium has not yet been demonstrated”.
The olfactory epithelium is more susceptible to the virus.
To get to the bottom of this, the team thus characterized the presence of ACE2 in tissue samples from different parts of the nasal mucosa taken from 23 patients without Covid-19 during endoscopic surgery for tumors or chronic rhinosinusitis (inflammatory diseases of the nose and paranasal sinuses). As well as the tracheal tissue of seven other people. If ACE2 is not present in the olfactory neurons that carry olfactory information from the nose to the brain (as previously shown in animals), then ACE2 is extremely abundant in the nose olfactory cells in the area responsible for the smell!
It has been shown that the surface of the olfactory sustentacular cells has 200 to 700 times more ACE2 than the epithelial cells of the nasal airways and the trachea. Therefore, the virus is more likely to bind and enter the olfactory cells than the respiratory cells. In other words, If a small amount of the virus enters the nose, the olfactory epithelium may be the most receptive place for the virus to settle.
In other words, these results suggest that this area of the nose could be the preferred entry route for the coronavirus (although there are others). Meifeng Chen: “The olfactory epithelium is a relatively easily accessible part of the body for a virus, and the very high levels of ACE2 we find there could explain why it is so easy to catch COVID-19.”
Why does the virus cause loss of smell? Professor Lane is well aware of this: “Once the virus begins to multiply, it most likely causes the destruction of the supporting cells that support the olfactory neurons and act as a protective barrier. Once lost, the neurons are also lost – leading to a loss of smell (and also taste, since most of the taste perception comes from the smell). Although the olfactory epithelium can regenerate itself, it may not be able to do so as long as infection and inflammation persist. »
The use of the mask under the nose is ineffective
The consequence of this discovery is that people with a diminished sense of smell should be watched more closely. “Many people infected with SARS-Cov-2 have no symptoms,” continues Professor Lane, “but they may have subtle olfactory deficits that they don’t notice. Therefore, “smell testing may be a possible way to identify asymptomatic carriers. And “if people infected with a small amount of the virus have no symptoms, they can still transmit it through their nasal breathing. It is therefore essential to wear a mask over your nose when you are with other people, even if you do not believe you are infected”.
“If the olfactory epithelium is a site of replication and release of viruses, a mask is essential to prevent transmission to others during nasal breathing,” says Lane. “I see many people every day who wear their masks incorrectly under their nose so that only the mouth is covered. If a virus escaped from the nose, it would be ineffective at protecting others.”
Finally, the authors suggest that antiviral therapy administered nasally would be more effective. See the nasal rinse! “Since the olfactory region of the nose can be the first entry site for the virus and viral replication, we suggest that nasal rinsing with saline solution could hypothetically destroy the virus and limit infection and reduce transmission,” said Professor Lane. However, he adds that this is not an official recommendation, since this hypothesis, which has not been confirmed, needs to be investigated and tested.