Introduce a new bison, and perhaps Johne's disease too.
A bison producer family managed a 100 head herd for breeding stock and meat. A cow introduced to the herd within the year had lost more than 300 pounds and had diarrhea. When the veterinarian completed a health check, the primary findings were positive results for two Johne's disease blood tests (i.e. antibody to M. paratuberculosis was detected by both AGID and ELISA. She was euthanized but no gross signs of the infection (such as enlarged lymph nodes or corrugated gastrointestinal tract) were found when the carcass was examined at necropsy. Tissues were collected (1) to be assessed microscopically for lesions caused by the infection and (2) to try to isolate the M. paratuberculosis organism from the tissues through culture.
Johne's disease was confirmed by both methods. The organism was isolated from many sites in the gastrointestinal tract (the ileum, jejunum, duodenum, cecum, colon, liver, mesenteric lymph nodes). M. paratuberculosis was also isolated from the animal's manure, meaning she had been shedding the organism on the premises.