Salmonellosis in a group of ponies: failure to identify a chronic active carrier.

Three of 33 ponies died after the herd had been moved to a new environment 3 months earlier. One mare died without premonitory signs of illness. Shortly thereafter, a 5-day-old foal and a 2-year-old gelding died after brief illness. Although cultures were not performed on the mare, Salmonella typhimurium was isolated from the feces and tissues of the foal and gelding. Lesions in the foal were confined to ecchymotic hemorrhages on the mucosal surface of the colon and petechial hemorrhages in the splenic capsule, with adhesions to the parietal peritoneum. The gelding had evidence of severe typhlitis and colitis. Subsequent culturing of feces from all ponies for 5 consecutive days revealed five ponies shedding S typhimurium, including the dam of the dead foal, the 6-week-old foal of the dead mare, and three others. Phage typing indicated that all isolants were of the same type. Weekly fecal cultures of all ponies for the next 9 weeks revealed that 1 month after the initial cultures, none of the ponies was shedding Salmonella. Monthly cultures for the next year did not yield any growth of Salmonella, indicating there was no active carrier (shedder) in the herd. The source of Salmonella that initiated the outbreak was not found, in spite of environmental culturing.