U.S. Food and Drug Administration

1. U.S. Food and Drug Administration Notice: Archived Document The content in this document is provided on the FDA’s website for reference purposes only. It was current when produced, but is no longer maintained and may be outdated.

2. Pathogen Shedding-Some Issues Richard Isaacson Department of Veterinary PathoBiology University of Minnesota

3. Take home points • Most farms have Salmonella • Shedding of Salmonella is sporadic • In healthy pigs, fecal/cecal concentration is low (10-100 per gram) • Apparently healthy pigs are carriers of Salmonella • Shipping, feed withdrawal, and lairage are important • Detection is difficult • Growth promoters don’t necessarily affect Salmonella in pigs • Salmonella can be acquired rapidly

6. Effect of repeated sampling • In slaughter plant samples (mesenteric lymph nodes) from 141 farms approximately 65% were found to contain Salmonella • Repeat sampling within one year found many of the negative farms were now positive and some positive farms were now negative (total positives approaching 90%) • After a third sampling, 95% of all farms were positive for Salmonella

8. Study Design • 46 post weanling pigs were challenged orally with 108 nalrSalmonella typhimurium. They were re-challenged at 4 weeks. • All were reared conventionally • At market weight (~240 lbs) they were divided into 4 groups • Group 1 remained on feed • Group 2 had feed withdrawal at 6 hours • Group 3 had feed withdrawal at 12 hours • Group 4 had feed withdrawal at 24 hours • All were shipped for 3 hours and necropsied

11. Detection of Salmonella is difficult • What is the sensitivity of the assay? • Do culture conditions affect detection? • What is the reproducibility of detection? • Repeated sampling

12. Some culture methods Method 3 Method 1 Method 2 1 gm feces in TTB 10 gm feces in BPW 1gm feces in GN Hajna RV broth RV broth RV broth XLT4 XLT4 XLT4 Biochem Biochem Biochem Davies, et al. J. Appl. Microbiol. 89:169-177 (2000)

13. Using method 1 and varying sample quantity Davies, et al. J. Appl. Microbiol. 89:169-177 (2000)

14. Comparison of laboratories and methods Davies, et al. J. Appl. Microbiol. 89:169-177 (2000)

15. Do growth promotants increase Salmonella typhimurium shedding? • 60 pigs were challenged orally with 108 nalrSalmonella typhimurium (MIC was >100 mg/ml) • The pigs were divided into two groups • Flavomycin (2 gm/ton) • No flavomycin • Pigs were reared conventionally to market weight (~240 lbs), subjected to 12 hours of feed withdrawal and ~3 hours of transport • Pigs were necropsied and S. typhimurium sought

17. Growth Promotion Effects of Flavomycin

18. Intranasal infection route • Fedorka-Cray showed that intranasal inoculuation of pigs resulted in Salmonella typhimurium being found in the gut within 3 hours • Fedoraka-Cray, et al, Infect. Immun.63:2658 (1995

19. Rapid Infection during lairage • Hurd showed that exposure to Salmonella typhimurium in feces leads to positive pigs held in a pen with contaminated feces • 2 hours post exposure 8/10 pigs were positive • 3 hours post exposure 6/10 pigs were positive • 6 hours post exposure 6/6 pigs were positive Samples included inguinal, ileocecal, and mandibular lymph nodes and cecal, ileal, and fecal samples Hurd, et al, AJVR 62:1194(2001)

20. Take home points-restated • Most farms have Salmonella • Shedding of Salmonella is sporadic • In healthy pigs, fecal/cecal concentration is low (10-100 per gram) • Apparently healthy pigs are carriers of Salmonella • Shipping, feed withdrawal, and lairage are important • Detection is difficult and not particularly sensitive! • Growth promoters don’t necessarily affect Salmonella in pigs • Salmonella can be acquired rapidly

21. Collaborators • Ronald Weigel • Peter Bahnson • Larry Firkins • Federico Zuckerman • Charles Francisco • National Pork Board • Illinois Council on Food and Agricultural Research • Hoechst Roussel Pharmaceuticals