PP1111 - Auditory Brainstem Responses in Infant Macaques with Exposure to Intrauterine Transmission of Zika Virus from Birth to Three Years of Age

Abstract:
Many different viruses can affect children’s hearing sensitivity if contracted during pregnancy. Research has shown that the transmission of the Zika virus in-utero causes congenital fetal abnormalities. Currently, there is little data available on the association between hearing loss and the Zika virus. Auditory Brainstem Response (ABR) testing on infant macaque monkeys can indicate whether or not hearing sensitivity is affected by the contraction of Zika virus. Analyzing the ABR responses can help determine the audiological effects of Zika virus and aid in improving future protocols.

Summary:

Rationale/

Purpose:
The emergence of the Zika virus as a public health concern in the United States in 2016 prompted investigations into its impact, particularly on infants exposed in utero (Centers for Disease Control and Prevention, 2019). While known effects include conditions such as microcephaly, the understanding of Zika's influence on hearing sensitivity in infants remains limited. This study explored the auditory function of infant macaque monkeys as a model for research due to their similarities to humans in various aspects. Understanding the association between Zika virus and the potential deficiency in hearing sensitivity allows for earlier planning and proper intervention. Research from animal models may provide insight into understanding the severity and progression of hearing loss associated with Zika Virus.

Methods:
In this study, twenty-five rhesus macaques exposed to Zika virus in utero were monitored using auditory brainstem response (ABR) testing completed at 3, 6, 12, and 36 months of age. Hearing thresholds were estimated using auditory brainstem responses to clicks, and 500 and 1000 Hz tone bursts. Previous research shows ABR testing is a reliable and valid measurement to test hearing sensitivity in macaques and is translatable to a human population.
All ABRs were completed with the Bio-logic Navigator Pro system using insert ER-3A earphones and subdermal electrodes placed behind the left mastoid, right mastoid, low forehead (ground), and high forehead (vertex). Clicks were recorded at 70, 50, and 30 dB nHL. Tone bursts at 500 and 1000 Hz were recorded at 80, 60, and 40 dB nHL. Each response was recorded twice for reliability, with the noise floor being less than 10% of sweeps. The infant macaque monkeys were sedated and monitored by a veterinarian technician.

Results:
Previous research has shown that only four waveforms are generated due to the smaller head size and auditory nerve in rhesus macaques (Møller et al., 1986). Due to this, wave IV was examined for threshold estimations in the subjects. The threshold is the lowest level (30 dB nHL for clicks and 40 dB nHL for 1000 and 500 Hz tone bursts) at which a response at wave IV could be identified. For click stimulus, all subjects had present responses at the lowest level tested (30 dB nHL) at 36 months of age
Conclusions:
The preliminary findings indicate no apparent link between Zika virus exposure in utero and atypical hearing sensitivity in infant macaque monkeys. All subjects had present responses to click stimuli at the 36-month interval of testing. Further analysis of the latency data aims to identify any atypical occurrences and contribute to a broader understanding of the Zika virus effects on auditory function in this non-human primate model.

Learning Objectives:

• Upon completion of this session, the participant will be able to demonstrate knowledge of how hearing is affected in Zika infected macaques from 3 months to 3 years of age.