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
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