Many COVID-19 patients have reported symptoms affecting the ears, including hearing loss and tinnitus.
Dizziness and balance problems can also occur, suggesting that the SARS-CoV-2 virus may be able to infect the inner ear.
In a new study from MIT and Massachusetts Eye and Ear, researchers found that the virus can indeed infect cells of the inner ear, including hair cells, which are critical for both hearing and balance.
They also found that the pattern of infection seen in human inner ear tissue is consistent with the symptoms seen in a study of 10 COVID-19 patients who reported a variety of ear-related symptoms.
In the study, the team used novel cellular models of the human inner ear that they developed, as well as hard-to-obtain adult human inner ear tissue.
In both the human inner ear samples and the stem-cell-derived cellular models, the researchers found that certain types of cells—hair cells and Schwann cells—express the proteins that are needed for the SARS-CoV-2 virus to enter the cells.
These proteins include the ACE2 receptor, which is found on cell surfaces, and two enzymes which help the virus to fuse with the host cell.
The human hair cells that the researchers studied were vestibular hair cells, which are involved in sensing head motion and maintaining balance.
Cochlear hair cells, which are involved in hearing, are much harder to obtain or generate in a cellular model. However, the researchers showed that cochlear hair cells from mice also have proteins that allow SARS-CoV-2 entry.
The pattern of infection that the researchers found in their tissue samples appears to correspond to the symptoms observed in a group of 10 COVID-19 patients who reported ear-related symptoms following their infection.
Nine of these patients suffered from tinnitus, six experienced vertigo, and all experienced mild to profound hearing loss.
While this study strongly suggests that COVID-19 can cause auditory and balance problems, the overall percentage of COVID-19 patients who have experienced ear-related issues is not known.
The researchers now hope to use their human cellular models to test possible treatments for the inner ear infections caused by SARS-CoV-2 and other viruses.
The study is published in Communications Medicine. One author of the study is Lee Gehrke.
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