PROGRESSION OF PNEUMOCYSTIS-CARINII INFECTION IN AN ANIMAL-MODEL

The development of infection in immunosuppressed rats is important not only in understanding the infection, but also as a source of P. carin ii antigen for use in diagnostic serological tests. The aims of this s tudy were to monitor the progression of P. carinii infection in the Sp rague Dawley rat model and then determine parameters that indicate the maximum production of P. carinii antigen. Seventeen Sprague Dawley ra ts were killed at intervals up to 9 weeks after the start of immunosup pressive therapy. The progression of P. carinii lung infection was obs erved by Giemsa staining of lung imprints and by a hemi-nested polymer ase chain reaction (PCR). Body weight, food and water intake and the a ppearance and activity of the rats were measured daily. Seven control rats were kept under the same conditions. P. carinii infection was det ected in the lung 2 weeks after immunosuppression by hemi-nested PCR a nd 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 greater than or equal to 6 weeks. Body weight was significantly greater in control rats than in the immunosup pressed 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 less than or equal to 9 used in conjunction with P. carinii dur ation of immunosuppression may be useful to maximise the yield of infe ction from individual rats.