Mycoplasma pulmonis-host relationships in a breeding colony of Sprague-Dawley rats with enzootic murine respiratory mycoplasmosis.

The longitudinal Mycoplasma pulmonis-host relationships in rats 1 to 72 weeks of age were investigated in a conventional breeding colony of Sprague-Dawley rats with enzootic murine respiratory mycoplasmosis (MRM). Mean intracage ammonia (NH3) concentrations of 52 +/- 21 micrograms/1 and active Sendai virus infections during the first month of life were associated with important early events in MRM. There was rapid colonization of proximal airways by large numbers of M. pulmonis in most rats by 2 weeks of age and the lungs by 6 weeks. The prevalence of lesions of MRM peaked by 3 weeks in nasal passages, later in middle ears, larynx and trachea, and not until 8 weeks in lungs. Approximately 10% of rats 8 weeks of age and older had bronchiectasis and/or bronchiolectasis, usually restricted to a few airways. Despite continued high NH3 concentrations (42 +/- 14 micrograms/1 in cages of weanlings and 86 +/- 45 micrograms/1 in cages of adults), M. pulmonis populations declined dramatically by 8 weeks of age. Nevertheless, in older rats lesions continued to be extremely prevalent in proximal airways. Mycoplasma pulmonis infection and disease persisted in respiratory tracts of most rats through 72 weeks of age, despite high serum concentrations of mycoplasma-specific IgM and IgG antibodies. These interrelationships of M. pulmonis, host, and environment may be representative of many breeding colonies of rats that have enzootic MRM.