SARS-CoV-2 infects cells in the inner ear.
- Certain types of cells in the inner ear express the proteins necessary for the SARS-CoV-2 virus to enter the cells.
- The virus can infect in particular hair cells and, to a lesser extent, Schwann cells.
- The overall percentage of Covid-19 patients who have had ear problems is not known.
Many Covid-19 patients have reported symptoms affecting the ears, including hearing loss and tinnitus. Others have reported dizziness and balance problems, suggesting the virus could infect the inner ear. A new study by researchers at MIT and Massachusetts Eye and Ear provides evidence that the virus can actually infect inner ear cells, including hair cells, which are essential for both hearing and balance. They published their results on October 29 in the journal CommunicationsMedicine.
Ear Infection Patterns
The researchers used new cellular models of the human inner ear that they developed, as well as human inner ear tissue. “Having the models is the first step, and this work now opens a way to work with not only SARS-CoV-2 but also other viruses that affect hearing.”, notes Lee Gehrke, who co-directed the study. Before the onset of the pandemic, researchers began work on a project to develop cellular models to study human inner ear infections. Viruses such as cytomegalovirus, mumps virus, and hepatitis viruses can all cause deafness, but exactly how they do it is not known.
These models allowed researchers to be able to study the effects of SARS-CoV-2 on the ears after virus-positive patients complained of hearing loss, tinnitus and vertigo. In samples from the human inner ear and in cell models derived from stem cells, the researchers found that certain types of cells – in this case hair cells and Schwann cells – express the proteins necessary for the virus to SARS-CoV-2 enters cells. These proteins include the ACE2 receptor, which is found on the surface of cells, and two enzymes – called furin and serine 2 transmembrane protease – that help the virus fuse with the host cell.
Pay increased attention to hearing problems
The researchers have thus shown that the virus can indeed infect the inner ear, in particular the hair cells and, to a lesser extent, the Schwann cells. In particular, it is the vestibular hair cells which are involved in detecting head movements and maintaining balance. Cochlear hair cells, which are involved in hearing, are much more difficult to obtain or generate in a cell model. However, researchers have shown, in mouse models, that they also contain proteins that allow SARS-CoV-2 entry.
Although this study suggests that Covid-19 can cause hearing and balance problems, the overall percentage of sufferers who have had ear problems is not known. “Initially, it was because screening tests were not readily available for patients who were diagnosed positive, and also, when patients had more life-threatening complications, they did not pay much attention to their hearing.concluded Konstantina Stankovic who co-directed the study. We still don’t know what the incidence is, but our results really call for more attention to audio-vestibular symptoms in people exposed to the virus..”
Multiple entry routes possible
The authors hypothesize that possible routes for the virus to enter the ears include the Eustachian tube, which connects the nose to the middle ear. “The virus could also escape from the nose through small openings surrounding the olfactory nervesbelieves Konstantina Stankovic. This would allow it to enter the brain space and infect cranial nerves, including the one that connects to the inner ear.”
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