For this research, scientists developed novel cellular models of the inner ear and used hard-to-obtain adult human inner ear tissue.
According to the study authors, limited availability of this tissue had hindered previous research into how SARS-CoV-2 and other viruses can damage hearing.
They found a pattern of inner ear infection consistent with symptoms observed in a study of 10 patients with COVID-19 who had reported a range of ear-related symptoms.
“Having the models is the first step, and this work opens a path now for working with not only SARS-CoV-2 but also other viruses that affect hearing,” Lee Gehrke, PhD, the Hermann L.F. von Helmholtz professor in MIT’s Institute for Medical Engineering and Science, who co-led the study said in a statement.
The study included 10 adult patients who tested positive for COVID-19 and developed symptoms that included hearing loss, tinnitus (ringing in the ear), or dizziness within 3 weeks of diagnosis.
Researchers analyzed inner ear tissue sourced from humans and mice to create in-vitro cellular models of the inner ear.
They discovered that both human and mouse inner ear tissue contained “molecular machinery to allow SARS-CoV-2 entry,” like the ACE2 receptor. Researchers also found that the virus could infect two types of cells in the inner ear called Schwann and hair cells.
“Our findings suggest that inner ear infection may underline COVID-19-associated problems with hearing and balance,” the study authors wrote.
“Vestibular hair cells serve as sensory receptors in the inner ear that function to assess and monitor head motion, a sense of balance, allowing humans and animals to orient themselves,” Dr. Robert Glatter, an emergency physician at Lenox Hill Hospital in New York, told Healthline.
“Schwann cells, also found in the specialized apparatus of the inner ear known as the
According to Glatter, the takeaway is that this study found that vestibular hair cells and Schwann cells express proteins that are essential for SARS-CoV-2 to enter cells.
“These proteins include the ACE2 receptor, which is found on the surface of cells,” he said, “and two enzymes called
According to the study authors, the developing inner ear is “notoriously sensitive” to congenital (born with) viral infection, and congenital
“Viruses such as CMV as well as HIV can lead to hearing loss,” said Glatter. “CMV accounts for up to 40 percent of congenital hearing loss.”
He added that HIV could also lead to hearing loss “via direct effects on ear structures or specialized ear cells themselves,” or indirectly, by suppressing the immune response that protects against bacterial or fungal infection.
Researchers noted that they observed SARS-Cov-2 infection of OPCs, a cell type present in the developing fetal inner ear.
Glatter emphasized the need to pay “extra” attention to symptoms like dizziness, hearing loss, and tinnitus in those exposed to COVID-19, as well as those who test positive for the coronavirus.
“While fever, loss of taste and smell, and respiratory symptoms may be more common in those ultimately diagnosed with COVID-19,” said Glatter, “neurological presentations including dizziness, hearing loss, vertigo, and stroke-like symptoms can also be important presenting symptoms of COVID-19.”
Some people with long COVID, also known as long-haul COVID-19, report
New research finds that cells in the ear are susceptible to infection with SARS-CoV-2, causing symptoms that include dizziness, ear ringing, and hearing loss.
Experts say that other viruses may also cause hearing loss, and newborns can be especially at risk.
They also say that while neurological symptoms of SARS-CoV-2 infection are less common, they’re still very important signs of disease that should be considered in those who test positive for, or are exposed to, COVID-19.