The objective of this study was to determine whether 2 distinct chlamydial isolates recovered from the intestines and feces of diarrheic nursery pigs could cause intestinal lesions in gnotobiotic pigs. Both isolates share biological characteristics with Chlamydia trachomatis. Chlamydial isolates R27 and R19 were propagated in Vero cells or embryonated eggs, respectively, and suspended in sucrose-phosphate-glutamine buffer with 10% fetal bovine serum for inoculation. Sham inocula were prepared from uninfected cell culture lysates and from uninfected eggs. Each piglet was fed 1 ml of inoculum or sham inoculum at 3-4 days of age. Ten piglets were each fed 109 inclusion-forming-units (IFU) and 14 piglets were each fed 106 IFU of isolate R27; 5 control piglets were fed sham inoculum. Twenty piglets were each fed 105 IFU R19; 5 control piglets were fed sham inoculum. All infected piglets developed diarrhea 4-5 days postinfection (DPI). Most piglets fed 109 IFU R27 became anorexic, dehydrated, and weak and were necropsied 4-7 DPI. Piglets fed 106 IFU R27 or 105 IFU R19 were necropsied 4, 7, 10, 14, and 18 DPI. Diarrhea, although never profuse, persisted in the piglets fed 106 IFU R27 or 105 IFU R19 through 12 DPI. At necropsy, all diarrheic piglets had watery colonic contents with flecks of undigested curd. In small intestine, histologic lesions were seen most consistently in distal jejunum and ileum. Distal jejunum and ileum from piglets fed 109 IFU R27 and necropsied 4-5 DPI were characterized by villus atrophy and multifocal necrosis of villi; necrosis was limited to the tips or apical one half of villi. Mild to severe villus atrophy, lymphangitis, and perilymphangitis were seen in the distal jejunum and ileum from all infected piglets 7 and 10 DPI. Colon from 1 infected piglet necropsied 10 DPI had mild focal serositis; significant colonie lesions were not seen in the other infected piglets. Immunostaining done on sections of distal jejunum and ileum revealed chlamydial antigen in villus enterocytes, occasional goblet cells, and occasional cryptai enterocytes and in foci of lymphangitis and perilymphangitis; the amount of detectable chlamydial antigen decreased after 4 DPI. In colon, sparse positive staining was seen in surface enterocytes and cryptai enterocytes. Ultrastructural examination of ileal villus enterocytes revealed chlamydiae, often together with glycogen particles, in vacuoles or occasionally free in the cytoplasm. The results indicated that the swine chlamydial isolates used in this study are intestinal pathogens in gnotobiotic pigs.
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