Progression of Pneumocystis carinii infection in an animal model.

The development of Pneumocystis carinii infection in immunosuppressed rats is important not only in understanding the infection, but also as a source of P. carinii antigen for use in diagnostic serological tests. The aims of this study were to monitor the progression of P. carinii infection in the Sprague Dawley rat model and then determine parameters that indicate the maximum production of P. carinii antigen. Seventeen Sprague Dawley rats were killed at intervals up to 9 weeks after the start of immunosuppressive therapy. The progression of P. carinii lung infection was observed by Giemsa staining of lung imprints and by a hemi-nested polymerase chain reaction (PCR). Body weight, food and water intake and the appearance and activity of the rats were measured daily. Seven control rats were kept under the same conditions. P. carinii infection was detected in the lung 2 weeks after immunosuppression by hemi-nested PCR and after 3 weeks by Giemsa staining. No P. carinii DNA was detected in any of the blood samples. Rats with moderate or severe lung infection had been immunosuppressed for > or = 6 weeks. Body weight was significantly greater in control rats than in the immunosuppressed rats. Six weeks of immunosuppression was used as a cut-off to determine measurements to identify those rats with moderate or severe infections in their lungs. A combination of > 34% body weight loss at 6 weeks after immunosuppression and the condition of the animals with scores < or = 9 used in conjunction with duration of immunosuppression may be useful to maximise the yield of P. carinii infection from individual rats.