The role of environmental ammonia in respiratory mycoplasmosis of rats.

Young adult, pathogen-free rats of Sherman and Fischer (F344) substrains were inoculated intranasally with 10(8) colony-forming units (GFU) of M. pulmonis and housed for 4 to 6 weeks in environments with ammonia maintained at specific concentrations from 25 to 250 ppm. All levels of NH3--whether produced naturally from soiled bedding or derived from a purified source--significantly increased the severity of the rhinitis, otitis media, tracheitis, and pneumonia (including bronchiectasis) characteristic of murine respiratory mycoplasmosis (MRM). The prevalence of pneumonia, but not that of other respiratory lesions of MRM, showed a strong tendency to increase directly with environmental NH3 concentration. In contrast, NH3 exposure of rats not infected with M. pulmonis caused anatomic lesions that were unlike those of MRM and were limited to the nasal passages. It was concluded that environmental NH3, at concentrations commonly encountered in present day cage environments for rats, plays an important role in pathogenesis of MRM.