Hearing loss in experimental cytomegalovirus infection of the guinea pig inner ear: prevention by systemic immunity.

Guinea pig cytomegalovirus (GPCMV) has been used to establish a reproducible model of viral labyrinthitis and hearing loss. Cochlear function was assessed by electrophysiological recordings of cochlear microphonic (CM) and eighth nerve N1 compound action potential (AP) thresholds prior to and up to eight days following inoculation of the scala tympani. Inner ear inoculation of seronegative subjects with live GPCMV produced profound elevations in CM and AP thresholds: 70% of these subjects had their thresholds raised to the limits of the sound system throughout the tested frequency range of 0.10 to 32 kHz. Histopathologic effects associated with CM and AP threshold shifts were primarily limited to the perilabyrinthine compartment, and were greatest in the most basal cochlear turns. Systemic infection with GPCMV produced an immune response, but did not affect CM or AP thresholds. Subsequent inoculation of the inner ear of these seropositive animals with live GPCMV did not result in either CM or AP threshold shifts, or cochlear histopathology. Inoculations of inactivated virus into the inner ears of seronegative and seropositive animals produced only moderate CM and AP threshold effects. Primary GPCMV labyrinthitis thus results in significant cochlear dysfunction and histopathologic changes which are prevented by prior systemic infection with GPCMV.