Study Reveals COVID-19 May Infect the Inner Ear

Understanding Hearing Loss in COVID-19 Patients

A recent study has unveiled that COVID-19 might infect the inner ear, providing insight into the hearing loss experienced by some patients after infection. This research, published in the journal *Nature Communications Medicine*, investigates the reasons behind symptoms such as hearing loss, tinnitus, and dizziness in individuals who have contracted COVID-19.

Examining Cochlea Functionality

The study involved ten COVID-19 patients exhibiting hearing loss-related symptoms. Out of these, six participants underwent hearing tests that confirmed the presence of tiny hair cells in the organ of Corti, which is responsible for hearing and located within the cochlea. All six patients demonstrated evidence of hair cell dysfunction, indicating that COVID-19 may impact these critical cells.

Pathways for Viral Entry into Inner Ear Cells

Researchers conducted analyses using a human-derived laboratory model to understand how the virus could infiltrate the inner ear. They obtained inner ear tissue samples from non-COVID-19 patients during ear surgery, a process that is typically challenging to achieve in clinical settings. Additionally, the team created inner ear models by converting skin cells into stem cells, which then differentiated into various types of inner ear cells.

Both the cochlea hair cells and Schwann cells, which surround nerves and form a protective myelin coating, were found to produce proteins that facilitate the entry of SARS-CoV-2 into human cells. A significant protein associated with these cells is angiotensin-converting enzyme two (ACE2), a receptor present on the surface of cells.

Other proteins identified in these hair and Schwann cells include furin cofactors and transmembrane protease serine two (TMPRSS2). These proteins assist the COVID-19 virus in merging with human cell membranes, enabling viral entry. The presence of ACE2, furin, and TMPRSS2 may explain how SARS-CoV-2 can access ear cells, establishing a connection between COVID-19 infection and hearing loss.

Potential Routes for Viral Transmission to the Ear

According to co-author Konstantina Stankovic, the virus could enter the inner ear through small passages in the nose that are linked to the nerves innervating the inner ear. Additionally, the virus may access the inner ear through the Eustachian tube, which connects the outer and inner ear. Stankovic is the Chair of the Department of Otolaryngology – Head and Neck Surgery at Stanford University.

Future Directions for Preventing Hearing Loss

Currently, effective treatments for hearing loss related to COVID-19 remain elusive and not clinically established. However, researchers are optimistic that the findings from this study will serve as a foundation for developing models to explore SARS-CoV-2 entry into human cells and ultimately create treatments for both COVID-19 infection and associated hearing loss.

References

1. Jeong, M. et al. (2021). Direct SARS-CoV-2 infection of the human inner ear may underlie COVID-19-associated audiovestibular dysfunction. *Communications Medicine Nature*, 1(44). doi: 10.1038/s43856-021-00044-w.

2. McDonnell, S. (2021). Study finds the SARS-CoV-2 virus can infect the inner ear. EurekAlert! Accessed on Nov. 4, 2021. Retrieved from https://www.eurekalert.org/news-releases/933025.