Intestinal lesions caused by a strain of Chlamydia suis in weanling pigs infected at 21 days of age

The objective of this study was to determine whether a strain of Chlamydia suis shown previously to be an intestinal pathogen in gnotobiotic piglets c ould cause diarrhea and intestinal lesions in young weanling pigs. Pigs fro m 2 sows were randomly assigned to 2 groups. Group 1 included 13 pigs that were weaned at 24 hours of age and then housed in isolator units and fed mi lk replacer and unmedicated starter ration. Group 2 included 8 pigs that nu rsed their respective sows, consumed unmedicated starter ration, and were w eaned at 21 days of age. Ten pigs in group 1 and 6 pigs in group 2 were ino culated orally with 4 x 10(8) inclusion-forming units of C. suis strain R27 at 21 days of age. Control pigs were inoculated with sham inoculum. The pi gs were necropsied 5-14 days postinoculation (DPT). None of the Chlamydia-i nfected pigs developed diarrhea. Villus atrophy was seen histologically in sections of ileum from Chlamydia-infected pigs in both groups 5 and 7 days DPI. Lymphangitis and multiple lymphohistiocytic and neutrophilic aggregate s were seen in the submucosa, tunica muscularis, and serosa of the distal j ejunum, ileum, and colon from Chlamydia-infected pigs in both groups 5-14 D PI. Immunostaining of sections of distal jejunum, ileum, and colon from inf ected pigs revealed chlamydial antigen in intestinal epithelium and in foci of lymphangitis/inflammation. The results indicated that C, suis strain R2 7 can cause intestinal lesions in young weanling pigs, and the lesions are similar to those seen in gnotobiotic piglets. The results also indicated th at strain R27 causes asymptomatic intestinal infections in young weanling p igs, at least under the conditions of this study.