The virus first establishes a foothold in the nasal area and can then move to the lungs, where it can cause more damage. Face masks can act as a roadblock in its path.
A research team at UNC-Chapel Hill sought to understand how the virus infects our the cells in our respiratory system and how it gets to the lungs, where it can cause pneumonia and wreak havoc on our organs.
In a set of lab experiments, the team used isolated SARS-CoV-2 viruses to see how the virus infects different types of cultured human stem cells. They found a striking pattern: the virus is most infectious to cells from the lining of the nasal passages. It then becomes less infectious to cells lining the throat, and even less infectious to lung cells. So the virus latches on to your nasal cavity, but if it is kept at bay there, it may be prevented from moving along to the lungs.
“If the nose is the dominant initial site from which lung infections are seeded, then the widespread use of masks to protect the nasal passages, as well as any therapeutic strategies that reduce virus in the nose, such as nasal irrigation or antiviral nasal sprays, could be beneficial,” said study co-senior author Richard Boucher, MD, the James C. Moeser Eminent Distinguished Professor of medicine and director of the Marsico Lung Institute at the UNC School of Medicine.
This might be explained by the fact that ACE2 -- the cell surface receptor that the virus uses to get into cells -- is more abundant in cells in the nasal lining, and far less abundant on the surface of lower airway cells.
Researchers suspect that the virus first settles in the nose, and then gets aspirated into the lungs, instead of expanding through the respiratory tract and "growing" from the nose. This is consistent with observations that people at higher risk from suffering severe lung disease (the elderly, the obese, and the diabetic) are much more prone to aspiration, especially at night during sleep. Wearing a face mask, even if imperfect, could prevent the viral particles from reaching the throat.
"These studies should provide valuable reference data for future animal models development and expand the pool of tissues, e.g., nasal, for future study of disease pathogenesis and therapy. While speculative, if the nasal cavity is the initial site mediating seeding of the lung via aspiration, these studies argue for the widespread use of masks to prevent aerosol, large droplet, and/or mechanical exposure to the nasal passages."
This could open up new avenues for treating COVID-19 -- potentially opening up a strategy of stalling it in the nasal cavity and preventing it from going down to the lungs.
In addition, the study could also help other teams devise better animal models, aiding in the further development of treatments and vaccines.
The study has been published in the journal Cell.
