1. ¹Department of Pathology, Hamamatsu University School of Medicine, Hamamatsu, Japan
2. ²Department of Otorhinolaryngology, Hamamatsu University School of Medicine, Hamamatsu, Japan

Correspondence: Professor Y Tsutsui, MD, PhD, Department of Pathology, Hamamatsu University School of Medicine, 1-20-1 Handayama, Higashi-ku, Hamamatsu, Shizuoka 431-3192, Japan. E-mail: ytsutsui@hama-med.ac.jp

Received 2 November 2007; Revised 27 February 2008; Accepted 7 March 2008; Published online 12 May 2008.

Abstract

Congenital cytomegalovirus (CMV) infection is the most common infectious cause of sensorineural hearing loss in children. Here, we established an experimental model of hearing loss after systemic infection with murine CMV (MCMV) in newborn mice. Although almost no viral infection was observed in the inner ears and brains by intraperitoneal (i.p.) infection with MCMV in newborn mice, infection in these regions was induced in combination with intracerebral (i.c.) injection of bacterial lipopolysaccharide (LPS). The susceptibility of the inner ears was higher than that of the brains in terms of viral titer per unit weight. In the labyrinths, the viral infection was associated with the mesenchymal vessels and accompanied by inflammatory cells induced by LPS, causing hematogenous targets of infection in the labyrinths. Viral infection also spread in the perilymph regions such as the scala tympani and scala vestibuli, probably from infected brains via meningogenic and cochlear nerve routes. Viral infection was not observed in the scala media in the endolymph, including the Corti organ. However, viral infection was observed in the spiral limbus, including the stria vascularis. These results suggest that hearing loss caused by labyrinthitis after congenital CMV infection may be enhanced by inflammation caused by systemic bacterial infection in the neonatal period.