The development of endolymphatic hydrops following CMV inoculation of the endolymphatic sac

The effect of inoculation of cytomegalovirus (CMV) into the endolymphatic sac was examined in CMV-seronegative and seropositive animals. Seronegative animals developed hearing loss, infection in the epithelial cells of the endolymphatic sac and perisaccular connective tissue, and endolymphatic hydrops. Control animals inoculated with inactivated CMV showed no hearing loss, viral infection, or endolymphatic hydrops. Seropositive animals showed complete protection from hearing loss and viral infection, yet a monocytic infiltrate was seen surrounding the endolymphatic sac. Associated with this localized immune response was mild evidence of endolymphatic hydrops in 40% (2/5) of the animals. Control seropositive animals inoculated with inactivated CMV showed no hearing loss or morphological changes. CMV then, can infect cells of the endolymphatic sac resulting in hearing loss and endolymphatic hydrops. The immune response to CMV in seropositive animals is protective, but is associated with endolymphatic sac inflammation.