In a new study published last month in the journal Nature Communications Medicine, the U.S.-based study authors wrote that they examined human inner ear tissue, human inner ear in vitro cellular models and mouse inner ear tissue to reach their conclusions.
Observing 10 COVID-19 patients with ear-related symptoms like hearing loss, vestibular dysfunction and tinnitus, the researchers said they had found a pattern of inner ear infection consistent with symptoms after developing some of the first human cellular models of infectious inner ear disease.
Using hard-to-get adult human inner ear tissue, the group found that both human and mouse inner ear cells have the “molecular machinery to allow SARS-CoV-2 entry.”
The virus could enter the ears using the eustachian tube, which connects the nose to the middle ear, or escape the nose through small openings surrounding the olfactory nerves, according to Konstantina Stankovic, a former Harvard Medical School associate professor and former chief of otology and neurotology at Massachusetts Eye and Ear.
Stankovic, who co-led the study, told MIT News that the virus could enter the brain space and infect cranial nerves, including the one that connects to the inner ear.
Furthermore, the researchers said that the infectious disease could infect hair cells and Schwann cells in the inner ear by using confocal microscopy.
“Our findings suggest that inner ear infection may be a significant cause of COVID-19-associated problems with hearing and balance,” they wrote.
Still, the overall percentage of COVID-19 patients with ear-related issues is unknown.
“Initially this was because routine testing was not readily available for patients who were diagnosed with [COVID-19], 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,” Stankovic said.
“We still don’t know what the incidence is, but our findings really call for increased attention to audiovestibular symptoms in people with [COVID-19] exposure,” she noted.
Stankovic told the outlet that the researchers now hope to use their human cellular models to test possible treatments for the inner ear infections caused by COVID-19 and other viruses.