Latent Pneumocystis carinii infection in commercial rat colonies: comparison of inductive immunosuppressants plus histopathology, PCR, and serology as detection methods.

Histopathologic evaluation combined with a period of immunosuppression has been the standard procedure for detection of Pneumocystis carinii in commercial rat colonies. Variation in induction regimens and in the sensitivity of detection methods may result in underreporting of the presence of P. carinii in breeding colonies or delay its detection. In the present study, methylprednisolone and cyclophosphamide were evaluated for the ability to induce P. carinii infection in rats from an enzootically infected commercial barrier colony. The presence of P. carinii was detected by histopathologic methods and by amplification of a targeted region of the P. carinii thymidylate synthase gene by PCR over the 8-week study period. Sera taken from rats prior to either induction regimen were evaluated for the presence of P. carinii-specific antibodies by the immunoblotting technique. Few significant differences in ability to induce organism burden or in histopathology were observed between the two immunosuppressive regimens. However, a dramatic loss of weight over the study period was observed in rats treated with methylprednisolone but not in rats treated with cyclophosphamide. Although histopathologic changes attributable to P. carinii did not appear before 2 weeks with either immunosuppressant, the presence of the organism in these animals was detected by immunoblotting and PCR. Cyst scores and the intensities of the histopathologic lesions increased during the study period, but the number of rats exhibiting evidence of P. carinii infection did not change after week 3. These results suggest that use of the PCR method on postmortem lung tissue of rats without prior induction regimens or identification of anti-P. carinii antibodies in antemortem serum samples is a sufficiently sensitive method for detection of the presence of a P. carinii carrier state in rodent breeding colonies.

Detection of Pneumocystis carinii in rats by polymerase chain reaction: comparison of lung tissue and bronchoalveolar lavage specimens.

The purpose of this study was to determine and compare the efficiency of detection of Pneumocystis carinii in rats by polymerase chain reaction (PCR) of DNA extracted from two sampling locations: lung tissue and bronchoalveolar lavage. The study involved naturally infected F344 rats that were allotted to groups to intercollate the investigation of several variables, including nonimmunosuppressed rats, rats subjected to a timed induction sequence of 1 to 4 weeks of immunosuppression, and two immunosuppressants: a corticosteroid and cyclophosphamide. The PCR amplified a 357-base pair region contained within the gene encoding the large ribosomal RNA subunit of P. carinii mitochondrial DNA. The identity of the PCR product was confirmed by Southern blot analysis with an oligonucleotide probe. In a comparison of lung bronchoalveolar lavage specimens after immunosuppression, P. carinii was detected by PCR in 100% of lung tissue but in only 87.5% of the lavage specimens. Lung tissue of three animals was test-positive when the corresponding lavage specimen was negative by PCR analysis. The PCR detected P. carinii in both types of specimens from the same two of three nonimmunosuppressed rats. In all there was 88% agreement of PCR results between the two sampling techniques. The difference in diagnostic outcome for the two specimen types was not statistically significant (Fisher's exact test). It was concluded that both specimen types were adequate for PCR detection of P. carinii in rats.

Effect of propoxur-impregnated pesticide tape on mouse cholinesterase levels.

Mice housed in polycarbonate cages, either with or without fiberglass filter bonnets, were exposed to propoxur-impregnated tape for 2 hours, 24 hours, or 7 days. Both erythrocyte and serum cholinesterase levels were determined at each time point. Body weights were also measured. There was no change in body weight or serum cholinesterase level. Erythrocyte cholinesterase level showed significant decrease, related to increasing length of exposure.