Experimental pneumococcal otitis media: longitudinal studies in the gerbil model.

In order to ascertain that the Mongolian gerbil, Meriones unguiculatus, is an acceptable model for studying the development of chronic from acute otitis media, we used previously published methods for experimental otitis media in a longitudinal study of the acute disease and sequellae. The gerbil was found to be susceptible to as few as 30 viable Streptococcus pneumoniae type 3 cells, indicating that only a few viable pathogens are able to cause the disease. Untreated experimental infections with S. pneumoniae type 23 resulted in a mild, self-limiting disease with little permanent sequellae, while S. pneumoniae type 3 produced severe disease characterized by an acute phase of from 2 to 3 weeks, followed by the development of new bone formation and a vascularized granulation tissue which persisted throughout the 13-week study. Viable pneumococci could be recovered from the middle ears for only two weeks. We conclude that the gerbil is a useful model for otitis media.