Latent Pneumocystis carinii Infection in Commercial Rat Colonies: Comparison of Inductive Immunosuppressants plus Histopathology, PCR, and Serology as Detection Methods

Abstract

Histopathologic evaluation combined with a period of immunosuppression has been the standard procedure for detection ofPneumocystis 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. cariniiin 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 ofP. 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 toP. 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. cariniiinfection 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. cariniicarrier state in rodent breeding colonies.

Histopathology of Pneumocystis carinii pneumonia in immunocompetent laboratory rats

“…Recently, inflammatory lesions have been observed in the lungs of immunocompetent laboratory rats, very similar to those previously described (6)(7)(8). Since P. carinii has been detected in a wide variety of commercial rat colonies (20,21), assessing the presence of Pneumocystis infections in rats is necessary prior to their experimental use. Based on the latest evidence indicating that P. carinii causes the infectious interstitial pneumonia that was previously attributed to RRV in laboratory rats (7,8), the present study investigated whether the lesions observed were caused by P. carinii infection.…”

Retrospective Analysis of Bacterial and Viral Co-Infections in Pneumocystis spp. Positive Lung Samples of Austrian Pigs with Pneumonia

“…spp. in the sense of a latent infection have already been described [ 38 ] and this phenomenon could also appear in pigs. In that case, P .…”

Pneumocystis carinii Causes a Distinctive Interstitial Pneumonia in Immunocompetent Laboratory Rats That Had Been Attributed to “Rat Respiratory Virus”

“…Finally, according to PCR test results reported by others, Pneumocystis were not detected in diseased rat lungs 36,38 and were very common in commercial rat barrier colonies. [22][23][24]47 In immunocompetent rats from the transmission experiments and an endemically infected barrier-room breeding colony, seroconversion to P. carinii coincided with the concurrent peaks of IIP and Pneumocystis infection. Subsequently, in association with increasing antibody titers, P. carinii was cleared from lungs and the lesions of IIP resolved.…”