Characterization of natural occurring Pneumocystis carinii pneumonia in pigs by histopathology, electron microscopy, in situ hybridization and PCR amplification.

: Macroscopic, histologic, ultrastructural, microbiologic, in situ hybridization (ISH) and PCR detection results in three 8-week-old pigs naturally infected with Pneumocystis carinii (PC) are described. All animals had a nonsuppurative interstitial pneumonia and intra-alveolar Pneumocystis organisms with foamy eosinophilic and PAS positive appearance. Ultrastructurally, PC trophozoites and cysts were observed in pigs No. 2 and No. 3, with the former being much more numerous. PC organisms were located on the alveolar surface or within the alveolar septa. Trophozoites had numerous filopodia and were thick-walled. Cysts had no or few filopodia, were thick-walled and contained intracystic bodies. Using non-isotopic ISH on formalin-fixed, paraffin-embedded lung tissue sections, PC DNA from pigs No. 2 and No. 3 hybridized with a probe specific for PC ribosomal RNA (rRNA). Using primers specific for mitochondrial rRNA gene (pAZ102-E/pAZ102-H), and for the internal transcriber spacers of ribosomal gene of PC, PCR methods amplified a product in the lung of pigs No. 2 and No. 3 using either frozen or formalin-fixed and paraffin-embedded lung tissue. DNA from Pig No. 1 samples did not amplify with any primer. This is the first time that molecular biology techniques (in situ hybridization and PCR) have been applied to the study of porcine pneumocystosis.