LUNG AND NASAL LESIONS CAUSED BY A SWINE CHLAMYDIAL ISOLATE IN GNOTOBIOTIC PIGS

The objective of this study was to determine whether a chlamydial isol ate recovered from nasal swabs from swine with pneumonia could cause p neumonia and rhinitis in gnotobiotic pigs. The identity of the isolate currently is unknown, but it shares characteristics with Chlamydia tr achomatis. After propagation in Vero cells and preparation of the inoc ulum (2.5 x 10(10) inclusion-forming units/ml), chlamydiae were instil led into nostrils (1.0 ml/nostril) and lungs (2.0 ml intralaryngeally) of 15 anesthetized 3-day-old gnotobiotic piglets. Five age-matched gn otobiotic piglets were anesthetized and sham infected with uninfected cell culture lysates. Two treated piglets were moribund and 2 were sev erely dyspneic prior to necropsy 7 days postinfection (DPI), whereas r emaining treated piglets showed mild dyspnea upon exertion throughout the study. All treated piglets developed diarrhea. All treated piglets necropsied 7-21 DPI had extensive consolidation in cranial, middle, a nd accessory lung lobes; a majority of these piglets also had extensiv e consolidation in the caudal lobes. Treated piglets necropsied 28 and 35 DPI had a lobular pattern of consolidation in all lung lobes. Hist ologically, lesions in lungs from treated piglets necropsied 7, 14, an d 21 DPI were characterized by bronchointerstitial pneumonia with foci of type II pneumocyte hypertrophy and hyperplasia; pneumocytes and br onchial and bronchiolar epithelial cells were markedly vacuolated. Alv eolar macrophages, peribronchitis, peribronchiolitis, and perivasculit is were seen in lungs from treated piglets necropsied 28 and 35 DPI; t hose necropsied 28 DPI also had foci of lymphohistiocytic and plasmacy tic infiltrates. Turbinate lesions in all treated piglets were charact erized by mild multifocal lymphoplasmacytic and occasionally neutrophi lic rhinitis. Immunohistochemistry detected chlamydial antigen in bron chial and bronchiolar epithelial cells, pneumocytes, and inflammatory cells in treated piglets necropsied 7, 14, and 21 DPI. Positive staini ng was limited to alveolar macrophages in treated piglets necropsied 2 8 and 35 DPI. Chlamydial antigen was detected in turbinate epithelial cells at all necropsy intervals. Ultrastructurally, chlamydiae were se en with glycogen particles in vacuoles or free in the cytoplasm of bro nchial and bronchiolar epithelial cells and pneumocytes. The results i ndicated that the chlamydial isolate used in this study is a pathogen in gnotobiotic pigs.