Coronavirus could cause hearing loss, damage hair cells in cochlea, studies suggest
This is not the first time the coronavirus has shown to affect ears.
A recent study, published in the journal JAMA Otolaryngology, suggests that the SARS-CoV-2 virus was isolated from the ears (particularly middle ear and mastoid bone) of two deceased COVID-19 patients.
The study suggested that a COVID-19 test must be done before an ear surgery for the safety of healthcare practitioners. It also pointed out that there may be many factors that affect the viral colonisation of the ear in a host and more studies are needed to understand the effects of COVID-19 on the ears.
However, this is not the first time the virus has shown to affect ears.
Hearing loss in COVID-19 patients
In an article, published in the American Journal of Otolaryngology in April, it was pointed out that an old female patient of COVID-19 in Thailand reported hearing loss which did not get better even after she recovered from the infection. The study suggested that it may have been due to the effect of the virus on the brain stem.
This was the first-ever case of hearing loss reported in a COVID-19 patient. Later, a group of researchers explained how the virus may damage the brain and cause hearing loss in the article, Comment on “Hearing loss and COVID-19 : A note”.
As per the article, the virus can travel to the brain through blood cells. Our brain has a lot of ACE2 receptors, the cell surface protein that SARS-CoV-2 uses to enter healthy cells. The temporal lobe (present on either side of the head) of the brain, which controls hearing, also has plenty of ACE2 receptors. When the virus affects this area, it releases cytokines, which, in turn, damages the hearing centres in the brain.
Another study, conducted on 20 confirmed but asymptomatic COVID-19 patients, indicated that the virus damages the hair cells in the cochlea. The cochlea is a spiral bone inside the ear that helps in hearing. The bone is hollow from the inside and has tiny hairs. These hairs convert the sound vibrations into electrical signals that are sent to the brain for interpretation.
In Turkey, a 38-year-old female patient with COVID-19 presented with otitis media (ear infection) without any other classical symptoms of the disease. The woman was not previously diagnosed with tinnitus (ringing in the ears) or ear pain (two of the symptoms of otitis media) and did not have any comorbidity. On conducting an audiometry study, she was also found to have some hearing loss.
Side effects of medicine or damage by the virus
A study done at the University of Ferrara, Italy, suggested that most drugs used for coronavirus treatment including hydroxychloroquine, chloroquine, remdesivir, azithromycin, favipiravir and lopinavir have toxic effects on the ears (ototoxic).
Ototoxicity can lead to problems like imbalance, hearing loss, and tinnitus. As per this study, the effects can be reversible or irreversible and occur after weeks of regular use.
The Iran study did mention that various drugs used for the treatment of the coronavirus disease have potential ototoxic side effects. However, most of the patients in this study did not have a history of use of any ototoxic drugs.
It has been previously indicated that various viral diseases can lead to mild to severe hearing loss. These include viruses like cytomegalovirus infection, rubella, measles, HIV and herpes simplex virus and more. The hearing loss caused due to viral infection can even be congenital (since birth) and it can affect one or both the ears.
In most cases, the hearing loss is caused due to damage to the auditory nerves or the inner ear and inflammation. However, a co-infection with a fungus or bacteria may also lead to hearing loss in patients with a viral disease.
Either way, more studies are needed to understand how the virus affects the ear and what exactly is causing hearing loss in COVID-19 patients.
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