THIS BLOG IS ALSO AVAILABLE AS AN AUDIO CAST
The more you learn about COVID-19 the more there is to dislike about it. The global death toll from the virus is now more than five million and for those who survive there can be long-term health consequences. We know COVID can attack the lungs, heart and brain. Now we are learning it can also mess up your ears causing hearing problems, ringing in the ear (tinnitus) and leave you dizzy.
Viral infections are a known cause of hearing loss and other kinds of infection. That’s why, before the pandemic started, Dr. Konstantina Stantovic at Massachusetts Eye and Ear and Dr. Lee Gherke at MIT had been studying how and why things like measles, mumps and hepatitis affected people’s hearing. After COVID hit they heard reports of patients experiencing sudden hearing loss and other problems, so they decided to take a closer look.
They took cells from ten patients who had all experienced some hearing or ear-related problems after testing positive for COVID and, using the iPSC method, turned those cells into the kind found in the inner ear including hair cells, supporting cells, nerve fibers, and Schwann cells.
They then compared those to cells from patients who had similar hearing issues but who had not been infected with COVID. They found that the hair and Schwann cells both had proteins the virus can use to infect cells. That’s important because hair cells help with balance and the Schwann cells play a protective role for neuronal axons, which help different nerve cells in the brain communicate with each other.
In contrast, some of the other cells in the inner ear didn’t have those proteins and so were protected from COVID.
In a news release Dr. Stankovic says it’s not known how many people infected with COVID experienced hearing issues. “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 audio vestibular symptoms in people with Covid exposure.”
The doctors are not sure how the virus gets into the inner ear but speculate that it may enter through the Eustachian tube, that’s a small passageway that connects your throat to your middle ear. When you sneeze, swallow, or yawn, your Eustachian tubes open, preventing air pressure and fluid from building up inside your ear. They think that might allow particles from the nose to spread to the ear.
The study is published in the journal Communications Medicine.
CIRM has funded 17 different projects targeting COVID-19, several of which are still active.
The Stem Cellar 
Clinical investigation showed that patients with Covid-19 infection had high infection rate in hair and Schwinn cells which located in inner part of ears but not to others. Hair cells are sensory receptors of both the auditory system and the vestibular system in the ears of all vertebrates. Through mechanotranduction, hair cells detect movement in their environment. In mammals, the auditory hair cells are located within the spiral organ of corti on the thin basilar membrane in the cochlear of the inner ear. The hair bundles or stereocilia protrude from the apical surface of the cell into the fluid-filled cochlear duct. The hair bundles are arranged as stiff columns that move at their base in response to stimuli applied to the tips. Mammalian cochlear hair cells are of two anatomically and functionally distinct types, known as outer and inner hair cells. Damage to these hair cells results in decreased hearing sensitivity and because the innear ear hair cells cannot regenerate, the damage is permanant. The function of inner hair cells transforms the sound vibrations in the fluids of cochlear into electrical signals that are then relayed via the auditory nerve to the auditory brain stem and auditory cortex. The outer hair cells mechanically amplify low-level sound that enter the cochlear. The amplification may be powered by the movement of their hair bundles, or by electrically driven motility of their cell bodies. This is so-called somatic electromotility amplifies sound in all land vertebrates. It is affected by the closing mechanism of mechanical sensory ion channels at the tips of the hair bundles. On the other hand, Schwinn cells have important roles to serve the myelination cell of the peripheral nerves system (PNS) and support cells of peripheral neurons. They are concentrically around the inner axon and function by insulating and provide nutrients to axon. Myelination increases conduction velocity along the axon, allowing for the saltatory conduction of impulses.
Clinical investigation showed that, a number of viral infections can cause hearing loss. Hearing loss induced by these viruses can be congenital or acquired, unilateral or bilateral. Certain viral infection can directly damage inner ear structure, other can induce inflammatory responses which then cause this damage and still others can increase susceptibility for bacterial and fungal infection, leading to hearing loss. Typically, virus-induced hearing loss is sensorineural , although conductivity and mixed hearing loss can be seen following infection with certain virus.
Current study showed that, most of patients infected with Covid-19 experience hearing loss. As Covid-19 virus has ability to develop high viral loads and release high levels of inflammatory cytokines. Therefore , high expression of viral entry proteins, such as ACE2 receptors on hair and Schwann cells of inner ear, may attract high load of viruses to attack them and high volume of inflammatory cytokines released by those viruses may damage and dysfunction the inner part of ear leading to hearing loss. Organoids develop from iPSCs provide good model to determine the mechanism of virus infection and cause hearing loss of ear.
Does anyone know if hearing loss is permanent and what is treatment for the hearing lost
Hi Maryann, like a lot of things releated to COVID, we really don’t know. Hopefully it is temporary but just how temporary is not clear.
But where is the explanation as to why? Is it the S1 spike protein?
Are there any remedies at this point to try?
Hi Rick,happily there are several therapies, as well as the vaccines, that have been approved to treat people with COVID.