A study from the researchers at MIT and Massachusetts Eye and Ear has provided evidence that the coronavirus can infect cells of the inner ear, including hair cells, which are critical for both hearing and balance, according to Science Daily.
The study, published in the journal Communications Medicine, also found that the infection in human inner ear tissue is consistent with the symptoms seen in a study of 10 patients with COVID who reported a variety of ear-related symptoms.
The researchers developed new cellular models of the human inner ear and studied the adult human inner ear tissue.
The study’s co-lead author Lee Gehrke, the Hermann L.F. von Helmholtz Professor in MIT’s Institute for Medical Engineering and Science, said, “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.”
Another co-lead author Konstantina Stankovic and lead author MinjinJeong were also part of the study.
Before the pandemic began, Gehrke and Stankovic were working together on a project to develop cellular models to study inner ear infections in humans.
Most viruses, including cytomegalovirus, mumps virus, and hepatitis viruses, have been associated with deafness, but it is unclear how exactly these viruses cause deafness.
However, the researchers altered their plans as soon as the pandemic began in early 2020.
At Massachusetts Eye and Ear, Stankovic saw COVID patients experiencing hearing loss, tinnitus, and dizziness. She said, “It was very unclear at the time whether this was causally related or coincidental, because hearing loss and tinnitus are so common.”
Stankovic and Gehrke decided to use the novel system they were working on to study COVID-19 infection.
They found that certain types of cells, hair cells and Schwann cells, express the proteins that are needed for the coronavirus to enter the cells. These proteins and two other enzymes called furin and transmembrane protease serine 2 help the virus to fuse with the host cell.
The team then found that the virus can actually infect the inner ear, specifically the hair cells and Schwann cells, causing tinnitus and hearing loss.
The hair cells that the researchers studied were vestibular hair cells, which are involved in sensing head motion and maintaining balance, according to Science Daily. Other hair cells, called cochlear hair cells, which are involved in hearing, were also affected.
Stankovic said, “Initially this was because routine testing was not readily available for patients who were diagnosed with Covid, and also, when patients were having more life-threatening complications, they weren’t paying much attention to whether their hearing was reduced or whether they had tinnitus.”
“We still don’t know what the incidence is, but our findings really call for increased attention to audiovestibular symptoms in people with Covid exposure,” she added.
She explained that potential routes for the virus to enter the ears include the Eustachian tube – the tube that connects the nose to the middle ear.
The virus may also enter olfactory nerves via the nose through small openings, further allowing it to enter the brain and infect cranial nerves, including the one that connects to the inner ear.
