The way humans perceive their world is mediated through sensory experiences. Of all the senses, it is hearing which fundamentally facilitates communication and fosters social interaction, allowing people to forge relationships, participate in daily activities, be alerted to danger, and experience life events.
Around 466 million people – 5% of the world’s population – live with hearing loss which is considered disabling; of these, nearly 34 million are children. The vast majority live in the world’s low-income and middle-income countries
Cytomegalovirus
Viral infections, in particular cytomegalovirus (CMV), cause up to 40% of all congenitally acquired hearing loss. CMV is an extremely common viral infection with nearly 100% prevalence. CMV is typically acquired early in life and maybe acquired in utero. In the United States, up to 1% of newborns are infected. CMV transmission to fetuses can occur during primary maternal infection (accounting for 40–50% of cases of congenital CMV) or reactivation during pregnancy (1% of cases of congenital CMV.
Congenitally acquired CMV is included as one of the TORCHS, an acronym for frequently occurring infectious teratogens (toxoplasmosis, rubella, CMV, herpes simplex, and syphilis, respectively). All of the TORCHS infections can cause similar signs before and after birth as well as similar birth defects. These include reduced intrauterine growth, microcephaly, seizures, mental retardation, visual defects, and cerebral palsy. Overall, the TORCHS is one of the most common causes of hearing loss that lead to pediatric cochlear implantation.
Maternal infection with CMV earlier in pregnancy increases the risk of symptomatic infection. CMV is the leading nongenetic cause of childhood Sensorineural hearing loss (SNHL).
Rubella
Rubella, also known as the German measles is most commonly transmitted via contaminated upper respiratory secretions during coughing, sneezing, and talking. If the virus is acquired during pregnancy it is a potent teratogen and one of the TORCHS infections. When a woman is infected with the rubella virus early in pregnancy, she has a 90% chance of passing the virus on to her fetus.
This can cause the death of the fetus, or it may cause Congenital rubella syndrome (CRS). CRS manifests as hearing loss, congenital cataracts, microcephaly, mental retardation, thrombocytopenia, cardiac anomalies, and a characteristic rash. SNHL is the most common sequela of congenital rubella infection (58%) and is most often seen when maternal rubella infection occurs within the first 16 weeks of pregnancy.
Lymphocytic Choriomeningitis Virus
Lymphocytic choriomeningitis virus (LCMV) has been identified as an emerging teratogen. Rodents, including the common house mouse, are the natural hosts and serve as reservoirs of LCMV. Infection is transmitted to humans through contact with rodent urine, feces, or saliva, and occurs more commonly in winter months when mice seek shelter indoors.
LCMV infection in pregnancy greatly increases the risk of spontaneous abortion. LCMV infection can also be teratogenic, especially if the virus is contracted during the first or second trimester, and is associated with microcephaly and hearing. In contrast to congenital CMV or rubella, visual impairment and microcephaly are much more common than hearing loss in congenital LCMV infection. LCMV can also be distinguished from these other congenital viral causes of hearing loss by the lack of hepatosplenomegaly.
Human Immunodeficiency Virus
HIV is the retrovirus that causes AIDS. The prevalence of auditory symptoms in patients with HIV is 14% to 49%. The risk of developing hearing loss increases with the patient’s age after the third decade of life. Infants can develop hearing loss following either infection or exposure in utero without.
Hearing loss in HIV-infected patients can be caused by a number of factors, including the direct effects of HIV, increased susceptibility to opportunistic infections in the middle ear and brain, and treatment with potentially ototoxic medications.
Herpes Simplex Virus (HSV)
HSV types 1 and 2 have been implicated as causes of hearing loss. Infection follows contact of mucous membranes or broken skin surfaces with infected fluids from herpes sores or with other body fluids of patients with herpes.
For HSV1, symptoms can include painful blisters on the lips and tongue that eventually rupture, dysphagia, fever, myalgias, and sore throat. In the case of HSV2 primary infection, symptoms include tingling in the affected areas, followed by an erythematous papular rash that evolves into blisters and then ruptured open lesions, as well as a viral prodrome and headache. The viruses can latently infect nerve cells innervating the initially infected tissue. Months to years later, the viruses can reactivate, leading to recurrent disease. HSV type 1 is typically associated with labial herpes and type 2 with genital herpes, although either virus can infect and manifest in the other’s typical territory.
HSV1 infection is much more frequently associated with encephalitis and hearing loss following infection in neonates compared with HSV2.
Measles (Rubeola)
The measles virus is very easily transmitted through contact with respiratory secretions from patients with measles. Hearing loss is a common complication of measles infection; prior to widespread vaccination, measles accounted for 5 to 10% of cases of profound hearing loss in the United States. Fortunately, most children recover from measles without long-term side effects.
Measles is associated with a high incidence of otitis media (in up to 8.5–25% of infected people, higher in developing countries), possibly due to a transient decrease in the immune response to infection. Sequelae of bacterial superinfection may account for some cases of hearing loss associated with measles infection.
Varicella Zoster Virus (VZV)
VZV first causes a primary infection that, when symptomatic, manifests with fever, an erythematous macular rash, and pustules (chickenpox).The virus can subsequently remain latent in neurons in various parts of the body for an extended period, reactivating years later. Symptoms of VZV reactivation (e.g., zoster or shingles) include both systematic symptoms (fever and malaise) as well as local symptoms (severe pain and a vesicular rash) that are limited to the area innervated by the neurons in which the virus reactivated. Risk factors for viral reactivation include age >50 years, pregnancy/postpartum states, and immunocompromise.
Reactivation of latent VZV within the geniculate ganglion causes Ramsay Hunt syndrome. Eighth nerve involvement results from the transfer of the virus from the nearby geniculate ganglion or directly from the facial nerve within the internal auditory canal. Symptoms include facial nerve paralysis, herpetic vesicles, severe otalgia, SNHL (24% of affected patients), tinnitus (48%), and vertigo (30%).
Mumps
Mumps is transmitted through infected respiratory secretions and is highly contagious. Mumps is one of the most common causes of acquired SNH.
Initially, mumps presents with symptoms of a flu-like illness, followed by bilateral swelling of the parotid glands. Mumps can additionally cause SNHL, pancreatitis, orchitis, oophoritis, and infertility. Aseptic meningitis and encephalitis can also occur, and their presence increases the risk of SNHL.
SNHL tends to occur suddenly 4 to 5 days after the onset of flu-like symptoms and parotitis. Typically, hearing loss is unilateral and reversible but can be severe and permanent.
The risk of SNHL following mumps infection is not correlated with the severity of the infection or presence of parotitis. Asymptomatic cases of mumps can result in sudden SNHL.
West Nile Virus
West Nile virus (WNV) is a member of the Flaviviridae family which also includes dengue and yellow fever virus. Viral transmission of WNV typically occurs through mosquito bites, but may also be acquired congenitally, through breastfeeding, or through blood transfusions from infected inpiduals. Hearing loss resulting from WNV infection is extremely rare.
COVID-19 and Hearing Loss
COVID-19, also known as the coronavirus, has now been linked to many long-term complications, including heart damage, lung damage, and neurological disorders. One emerging area of research is whether hearing loss and tinnitus (ringing in the ears) can result from coronavirus infection—either as a symptom or as complication days or weeks later. We do know that many different types of viral and bacterial infections can cause sudden hearing loss. But older coronaviruses that triggered epidemics, such as SARS and MERS, did not appear to cause hearing problems. More research is needed before we fully understand how the coronavirus affects hearing and balance.
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