Exacerbation of Murine Respiratory Mycoplasmosis in Gnotobiotic F344/N Rats by Sendai Virus Infection

Abstract

Six- to eight-week-old gnotobiotic F344/N rats were inoculated intranasally with 100.2 colony-forming units of Mycoplasma pulmonis or were sham inoculated, then one week later were given 100.2 50% tissue culture infective doses of Sendai virus or sterile medium. Groups of rats were killed immediately after virus inoculation and three, five, ten, and 20 days later. Lesions in nasal passages, middle ears, larynxes, tracheas, and lungs from half of the rats in each group were subjectively scored. Organs from the other rats were quantitatively cultured for M. pulmonis and for Sendai virus. Rats given Sendai virus alone had mild, patchy, necrotizing rhinitis, laryngitis, tracheitis, and bronchitis, but not bronchiolitis or interstitial pneumonia. M. pulmonis alone induced mild lesions of murine respiratory mycoplasmosis including mild to moderate suppurative rhinitis, otitis media, laryngitis, and tracheitis with submucosal lymphoid accumulation and epithelial hyperplasia, but not lung lesions. Rats given M. pulmonis and Sendai virus had severe lesions characteristic of advanced mycoplasmal disease throughout the respiratory tract, including suppurative bronchitis with extensive lymphoid accumulations and epithelial hyperplasia; some rats also had suppurative pneumonia and bronchiectasis. Larger numbers of M. pulmonis colony-forming units were in rats given Sendai virus, but there was no statistically significant difference in Sendai virus infectious units between rats also given M. pulmonis and those given virus only.