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.
The researchers evaluated hearing functions in seven male and six female infants born between July 2015 and February 2016. These infants were presumed to have developed microcephaly (head circumference 29.8 ± 3.2) as a result of Congenital Zika Syndrome during an outbreak in Bahia, Brazil. The infants were classified as: having evidence of Zika virus infection (2 infants), highly probable (4 infants), moderate probable (5 infants), or somewhat probable (2 infants).
All of the mothers whose infants were evaluated in the study reported exanthema during pregnancy, except for one. In 11 out of the 12 fetuses, prenatal ultrasounds showed intracranial calcifications and ventriculomegaly, said Dr. Boaventura.
Progressive unilateral sensorineural hearing loss was reported in two of the infants who presented with severe microcephaly. In another patient there was a delayed onset of hearing loss. Abnormal audiologic exam results were observed in six of the 13 cases, and auditory neuropathy in three.
“Something interesting we saw [was] that the Otoacoustic Emission test was normal in three of those babies… The ABR exam [showed] that the cochlea was [normal], but the acoustic nerve is not.” These results can help the researchers understand the level of lesions, which appears to be in the region of the lateral lemniscus.
ABR and OEA exams for the remaining cohort “did not correlate reliably with behavioral auditory thresholds that suggested a delay in hearing development in all cases.”
Dr. Boaventura concluded that “Zika virus infection may cause progressive and late-onset hearing loss in babies. Auditory neuropathy can be detected in Zika virus congenital infection. And conductive hearing loss may be associated with sensorineural disorders and aggravate hearing impairment." The team intends to conduct more auditory exams before publishing their results.
First International Conference on Zika Virus
Session 4: Clinical Spectrum
Prospective Evaluation of Hearing Function After Presumably Congenital Zika Virus Infection