Immunological, physiological and behavioral effects of Salmonella enterica carriage and shedding in experimentally infected finishing pigs

Authors: Rostagno, Marcos; Eicher, Susan; Lay Jr, Donald

Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2010
Publication Date: 5/1/2011
Citation: Rostagno, M.H., Eicher, S.D., Lay Jr, D.C. 2011. Immunological, physiological and behavioral effects of Salmonella enterica carriage and shedding in experimentally infected finishing pigs. Foodborne Pathogens and Disease. 8(5):623-630.

Interpretive Summary: Finishing pigs infected with Salmonella pose significant food safety risks by carrying the pathogen into abattoirs. This study was conducted to determine the dynamic of Salmonella infection in finishing pigs, and associated immunological, physiological, and behavioral alterations, by longitudinally comparing infected to non-infected pigs during 6 wk post-infection. Bacteriological data revealed that all inoculated pigs started shedding Salmonella within 2 hours post-infection, and persistently shed the bacteria up to the end of the study. Ileal and cecal contents, as well as mesenteric lymph node samples were all positive throughout the study, containing high levels of Salmonella up to 4 weeks post-infection. Interestingly, levels of Salmonella dropped markedly in all samples at 5 weeks post-infection. There was no difference between groups for blood cell counts. Inflammatory cell communication molecules were greater in infected pigs and progressed through the intestine and associated immune tissues in a predictable manner. Other cell communication molecules that drive the type of response and antimicrobial peptides that naturally control bacterial populations did not differ between infected and control pigs, but varied over time. Infected pigs spent more time lying sternally, standing, and sitting than controls. Infected pigs were also more active, and approached a novel object more quickly than control pigs. No treatment differences were detected for rectal temperature or plasma cortisol. This study shows that finishing pigs can carry high levels of Salmonella for up to 4 weeks post-infection in the gastrointestinal contents and mesenteric lymph nodes, shedding high levels of the bacteria without developing clinical symptoms. However, subtle behavioral changes measured as postures were detected, and therefore warrant additional investigation as a potential way of identifying infected pigs.

Technical Abstract: Finishing pigs infected with Salmonella pose significant food safety risks by carrying the pathogen into abattoirs. This study was conducted to determine the dynamic of Salmonella infection in finishing pigs, and associated immunological, physiological, and behavioral alterations, by longitudinally comparing infected to non-infected pigs during 6 wk post-infection. Bacteriological data revealed that all inoculated pigs started shedding Salmonella within 2 h p.i., and persistently shed the bacteria up to the end of the study. Ileal and cecal contents, as well as mesenteric lymph node samples were all positive throughout the study, containing 3 to 4 log10 cfu/g of Salmonella at 24 h p.i., and 4 to 5 log10 cfu/g of Salmonella up to 4 wk p.i. Interestingly, levels of Salmonella dropped markedly (P<0.05) in all samples at 5 wk p.i. There was no difference between groups for blood cell counts. Tumor necrosis factor-a was greater (P<0.05) in infected pigs: 1) in the mesenteric lymph nodes by 48 h p.i.; 2) at 24 h and 3 wk p.i. in the ileum; and 3) in the cecum and spleen by 3 wk p.i. Interleukin-12, IL-1 and its antagonist, and a porcine specific antimicrobial peptide RNA expression in tissues changed over time, but were not different between groups. Infected pigs spent more time lying sternally, standing, and sitting than controls (P<0.01). Infected pigs were also more active (P<0.01), and approached a novel object more quickly than control pigs (P<0.05). No treatment differences were detected for rectal temperature or plasma cortisol (P>0.10). This study shows that finishing pigs can carry high levels of Salmonella for up to 4 wk p.i. in the gastrointestinal contents and mesenteric lymph nodes, shedding high levels of the bacteria without developing clinical symptoms. However, subtle behavioral changes measured as postures were detected, and therefore warrant additional investigation as a potential way of identifying infected pigs.