LIMITED PERSISTENCE IN AND SUBSEQUENT ELIMINATION OF PNEUMOCYSTIS-CARINII FROM THE LUNGS AFTER PNEUMOCYSTIS-CARINII PNEUMONIA

The purpose of this study was to determine the period of persistence o f Pneumocystis carinii in the lungs after P. carinii pneumonitis (PCP) , After primary PCP was induced with dexamethasone, experimental rats were moved to a high-efficiency particulate air-filtered isolator to p revent further exposure to environmental P. carinii and allowed to rec over, At intervals thereafter, sample groups were transferred to a sec ond isolator and reimmunosuppressed with dexamethasone to provoke PCP if P. carinii were present. Reactivation of PCP was assessed by histol ogic examination, counts of cysts per gram of lung, and DNA amplificat ion using nested polymerase chain reaction. A sequential and progressi ve decrease in P. carinii was detected, Thus, P. carinii is cleared fr om the lungs of greater than or equal to 75% of animals within 1 year after an episode of PCP, implying that persistence of latent organisms is limited.