There’s still a great deal to know about COVID-19. It’s hard to believe, but it’s already been with us for over two years (but what a long two years it’s been). But unlike diseases that have been researched for decades, the medical community is still just scratching the surface of what there is to know about COVID-19.
The potential aftereffects of the virus on hearing are one area that still needs to be better understood. But preliminary information is troubling.
The fact that COVID-19 is not exclusively a respiratory ailment is at the core of potential hearing issues. Many people who get COVID-19 are struck with neurologic and heart-related problems. And the auditory system is deeply dependent on both the nervous and circulatory systems.
Any decrease in the efficient transfer of oxygen through the bloodstream can cause problems, or even permanent damage, to the workings of the inner ear. Likewise, any disruption with the complex nerve relays between the ear’s core and the brain’s auditory cortex can bring about hearing problems both temporary and enduring.
Then there’s the more direct risk of the virus spreading to the inner ear itself and causing damage. Many other viruses can do this and it’s a rosy scenario to believe COVID-19 can’t.
Hearing loss has already been reported following COVID-19 infection, but new study from the Massachusetts Institute of Technology (MIT) and Massachusetts Eye and Ear has been able to dissect what happens when the coronavirus affects the inner ear.
The study, which was just published in the journal Communications MedicineTrusted Source, looked at cellular models of the human inner ear and adult human inner ear tissue infected with SARS-CoV-2 to see what effect it had.
According to the findings, the ear is yet another region of our bodies that may be infected with SARS-CoV-2, the virus that produces COVID-19.
“This article provides very compelling evidence that SARS-CoV-2 infects the inner ear and may be causally related to hearing and balance symptoms in a number of patients with COVID-19 infection,” said Dr. Yuri Agrawal, an otolaryngology-head and neck surgery professor at Johns Hopkins School of Medicine who was not involved in the study.
Research Helps With Understanding the Relationship Between SARS-CoV-2 (and Other Viruses) and the Ear
Scientists created unique cellular models of the inner ear for this study and employed difficult-to-obtain adult human inner ear tissue.
Previous research into how SARS-CoV-2 and other viruses can harm hearing has been hampered due to a scarcity of this tissue, according to the study’s authors.
They discovered a pattern of inner ear infection compatible with symptoms documented in a study of 10 COVID-19 patients who reported a variety of ear-related symptoms.
“Having the models is the first step, and our work offers a way now for working not only with SARS-CoV-2 but also with other viruses that damage hearing,” said Lee Gehrke, PhD, the Hermann L.F. von Helmholtz professor in MIT’s Institute for Medical Engineering and Science, who co-led the study.
The research included ten adult patients who tested positive for COVID-19 and had symptoms such as hearing loss, tinnitus (ringing in the ears), or dizziness within three weeks of being diagnosed.
To generate in-vitro cellular models of the inner ear, researchers examined inner ear tissue from people and mice.
They uncovered “molecular machinery that facilitates SARS-CoV-2 entrance” in both human and animal inner ear tissue, such as the ACE2 receptor. The virus might also infect two types of cells in the inner ear termed Schwann and hair cells, according to the researchers.
“Our findings show that COVID-19-associated hearing and balance impairments may be exacerbated by inner ear infection,” the study’s authors concluded.
Schwann and Vestibular Hair Cells
“Vestibular hair cells act as sensory receptors in the inner ear that operate to measure and monitor head motion, a sense of balance, allowing people and animals to orient themselves,” said Dr. Robert Glatter, an emergency physician at New York’s Lenox Hill Hospital.
“Schwann cells, which are also located in the specialized inner ear mechanism known as the cochlea, are essential for hearing,” he stated.
The study discovered that vestibular hair cells and Schwann cells express proteins that are required for SARS-CoV-2 to enter cells, according to Glatter.
“Among these proteins are the ACE2 receptor, which is present on the surface of cells, and two enzymes termed furin and transmembrane protease serine 2 (TMPRSS2), which allow SARS-CoV-2 to adhere to the host cell,” he explained.
According to new research, cells in the ear are susceptible to SARS-CoV-2 infection, resulting in symptoms such as dizziness, ear ringing, and hearing loss.
Other infections, according to experts, may also cause hearing loss, and babies are especially vulnerable.
They further state that, while neurological symptoms of SARS-CoV-2 infection are less common, they are nonetheless highly relevant indicators of disease that should be taken into account in persons who test positive for or are exposed to COVID-19.