Acute Streptococcus pneumoniae Meningogenic Labyrinthitis: An Experimental Guinea Pig Model and Literature Review

OBJECTIVE: To create an experimental model of Streptococcus pneumoniae type 3 meningogenic labyrinthitis (a leading cause of deafness) similar to that in human disease. DESIGN: Cohort analytic study of guinea pigs that were inoculated intrathecally with varying dilutions of S pneumoniae type 3; the progress of the disease was compared with that in saline solution-inoculated control animals. SUBJECTS: Healthy adult Hartley guinea pigs without clinical evidence of middle ear disease that were conveniently sampled. INTERVENTIONS: Intrathecal inoculation of 10(4) to 10(6) colony-forming units of S pneumoniae type 3 into 13 guinea pigs; signs and symptoms of meningitis/labyrinthitis were observed for 15 days and compared with those in two saline solution-inoculated control animals. MAIN OUTCOME MEASURES: Morbidity--labyrinthitis, meningitis; end point--death. RESULTS: The 10(4) to 10(6) colony-forming units of S pneumoniae type 3 caused inflammation that extended from the meninges to the inner ear via the cochlear aqueduct within 3 days after inoculation; a dose of 10(7) killed animals within 12 hours after inoculation. Three of five animals that were inoculated with a 10(6) dose died 3 days after inoculation; two of three animals that were inoculated with a 10(5) dose lived to 15 days after inoculation. One of two animals that were inoculated with a 10(4) dose did not become infected. Inflammation extended to the middle ear by round-window destruction. Reactive bone formation simulated labyrinthine osteosclerosis. Observers assessed histologic slides "blindly." CONCLUSION: Guinea pigs can survive 15 days after intrathecal inoculation of a 10(5) dose, with morphologic features similar to those in human disease. This is an effective model for this study of meningogenic labyrinthitis.