Clinical and pathological observations on the experimental passage of swine dysentery.

The length of incubation for 36 eight and 12 week old swine in eight experimental passages averaged 11 days and ranged from five to 24 days. The duration of diarrhea for 24 of these swine averaged 6.4 days and ranged from two to 19 days. The consistent macroscopic lesion was a colitis and, subsequently, a typhlitis. In the swine euthanized on the first day of diarrhea, the colitis was most intense in the coils near the apex of the colon and, frequently, these swine had a hyperemia of the fundus of the stomach. The amount of visible blood in the colon varied. Organisms identified microscopically and ultrastructurally as spirochetes were observed commonly in the feces and the mucosal glands of the colon of swine with a diarrhea, but not in the adjacent mesenteric lymph nodes. These spirochetes which were the most numerous on the first day of diarrhea, could not be isolated and propagated in vitro. Swine which recovered naturally or were medicated at the height of a diarrhea, developed a resistance to swine dysentery. Colon from infected swine remained infectious when stored at -77 degrees C for nine months but not when stored at -16 degrees C. Feces from infected swine were not infectious after lyophilization and storage at -12 degrees C.