Otitis interna is a frequent sequela to Streptococcus suis meningitis in pigs

Twenty-eight histologically confirmed cases of porcine leptomeningitis were examined retrospectively, with focus on the pathology of the inner and middle ear, brain, and vestibulocochlear nerve. Tissues were evaluated by histology and immunohistochemistry for Streptococcus suis serotype 2 antigen, and the bacteriologic results were recorded. Exudative otitis interna was diagnosed in 20/28 pigs (71%). The lesions primarily affected the perilymphatic ducts, with consistent involvement of the scala tympani. Perineuritis of the vestibulocochlear nerve was seen in all but four of the ears affected with otitis interna. Immunohistochemically, S. suis serotype 2 antigen was demonstrated in the leptomeningeal, perineural, and labyrinthine exudates in 11 cases. Otitis media was diagnosed in 10/28 pigs (34%), but evidence of extension to the inner ear was not observed. The findings were highly similar to descriptions of meningogenic labyrinthitis in humans and in laboratory animal models. Otitis interna in pigs can also develop via the meningogenic route and is not always, as generally stated, tympanogenic.