We’ve heard that the virus that causes COVID-19, called SARS-CoV-2, can affect the toes and even the tongue. Now evidence from Massachusetts Institute of Technology (MIT) and Massachusetts Eye and Ear supports claims from many patients who say the virus is also impacting their ears. 

A report in Communications Medicine has investigated the underlying workings of COVID ear, a condition marked by hearing loss, tinnitus (a constant ringing in the ear), sudden loss of balance, extreme dizziness, and other symptoms. Their findings suggest that SARS-CoV-2 can infect the inner ear.  

What The Researchers Did

To see how SARS-CoV-2 might get inside the inner ear, the researchers first tested the ability of the virus to infect human inner-ear tissue. They then generated sustainable study models for future experimentation.

1.  Testing SARS-CoV-2 on Human Ear Cells

Using human inner-ear tissue left over from surgery, the researchers found that both hair and Schwann cells of the inner ear make the proteins needed for SARS-CoV-2 infection. 

Angiotensin-converting enzyme 2 (ACE2) is a receptor protein that allows the spike (S) protein of the virus to bind to the host cell, where two other enzymes (FURIN and transmembrane protease serine 2) split the spike protein shell to allow the virus entry. 

The researchers then tested how these cells would respond to SARS-CoV-2 versus a placebo solution.

2.  Developing Sustainable Study Models of Inner-Ear Infection

So other researchers might avoid the difficulty in accessing fresh inner-ear tissue, new study models were developed using cells outside the ear. Through genetic instructions, the researchers cleverly reverse-engineered skin cells into pluripotent stem cells, or cells that haven’t yet specialized and are capable of becoming any kind of cell. 

They slowly guided these stem cells to resemble the ear’s hair and Schwann cells. Two- and three-dimensional models were created; in the 3-D model, both cell types were cultured together to mimic the natural ear.

What They Found

In the first experiment, human inner-ear cells exposed to SARS-CoV-2 showed clear signs of viral infection (replication), whereas cells exposed to the placebo did not.

In the second experiment, all three proteins were found in the three-dimensional model of the inner ear, similar to the inner-ear tissue sample, as well as in the two-dimensional hair cell model. They were not all present in the two-dimensional Schwann cell model.

• In the inner-ear sample, vestibular hair cells that aid balance and sense head movement were found to be especially susceptible to SARS-CoV-2, with a 26% infection rate.
• Though not included in the study, the researchers suspected that cochlear hair cells, which detect sound and are similar to vestibular hair cells, would also be vulnerable to infection. Studies in mice support this theory, showing all proteins needed for infection.

What It Means

It isn’t yet known how the virus gains entry into the inner ear. One theory the authors have is that SARS-CoV-2 may travel through the nose, then into the olfactory bulb and the central nervous system, where it might follow the path of a cranial nerve.

Evidence of actual inner-ear infection by SARS-CoV-2 is still needed, but the study points to hair cells of the inner ear being susceptible to infection and damage, leading to the hearing and balance loss seen in COVID-19, and it provides a strong foundation for future research.

*Haseltine, W.A. (2021, November 18). Covid Ear: Virus Implicated. Forbes. https://www.forbes.com/sites/williamhaseltine/2021/11/18/covid-ear-virus-implicated/?sh=4e129f2f49

Much about the novel coronavirus, i.e., COVID-19, is still not fully understood. As research progresses and our knowledge of the virus increases, information can change rapidly. We strive to update all of our articles as quickly as possible, but there may occasionally be some lag between scientific developments and our revisions.