Updated March 1, 2017 at 8:27 PM EST
On Friday February 24, 2017 at the First International Conference on Zika Virus, Viviane S. Boaventura, MD, PhD, researcher, Fiocruz-Bahia, Gonçalo Moniz Institute, Brazil, presented her research on auditory impairment developing as a result of Congenital Zika Syndrome
Dr. Boaventura set the stage by giving a brief background on cases in which individuals exhibited auditory complications while presumably infected with the Zika virus—these included cases in adults and infants. The first patient to develop hearing loss possibly due to Zika was reported to be a 45-year-old female who was infected in Malaysian Borneo in 2014. The patient suffered “bilateral hearing difficulties during the course of illness,” 5 days after symptom onset. A letter
describing the case was published in the Centers for Disease Control and Prevention’s Emerging Infectious Diseases
journal. Dr. Boaventura then went on to discuss another study
, which she co-authored, that also outlined three cases in which adults who were either confirmed or suspected of Zika virus infection presented with transient hearing loss. Furthermore, a recent study noted that 5.8% of infants born with Congenital Zika Syndrome displayed hearing loss.
Using this information, Dr. Boaventura and colleagues conducted a prospective study to evaluate auditory function in infants with Congenital Zika Syndrome. The study looked at hearing functions in 13 infants with “microcephaly and presumed [Zika virus] infection in the first year of life.” The researchers conducted Otoacoustic Emission tests (OAE), “a screening exam to look for the function of the cochlea.” According to Dr. Boaventura, a previous study demonstrated that 3 out of 32 babies presented with altered OAE. However, although the team was able to confirm that hearing loss was related to the Zika virus, they "did not exclude external or middle ear disorders that could cause a negative OAE test not related to Zika virus infection."
Dr. Boaventura's team looked at the results of another study that used Auditory Brainstorm Response (ABR) tests to evaluate the function of the cochlea and the acoustic nerve. The researchers on this study
found that out of 70 infants, 6% to 7% had sensorineural hearing loss, which seemed to be related to the severity of the microcephaly, according to Dr. Boaventura. “Unfortunately, they didn’t evaluate … Behavioral Observational Audiometry (BOA),” which looks for response to sounds, such as eye movements.
Even after reviewing these studies, Dr. Boaventura and her team felt that some questions still remained unanswered, including: is hearing loss that is related to Congenital Zika Syndrome progressive? Is there any delayed onset of hearing loss related to Congenital Zika Syndrome?
Describing the research process, Dr. Boaventura said, “We performed this longitudinal study to investigate hearing function after Zika virus congenital infection. We looked for babies that had abnormalities in their [pre-natal] ultrasound exam, and then we collected blood samples, performed the otolaryngologist evaluation and a query in order to rule out other causes of hearing loss, like alcohol abuse. We then did a tympanometry test to evaluate the middle ear, and then we performed the first Otoacoustic Emission test and the ABR test.” The team also conducted a BOA evaluation, as well as other tests.