Immunological, physiological, and behavioral effects of Salmonella enterica carriage and shedding in experimentally infected finishing pigs
Posted: January 25th, 2011 - 1:54pm
Source: Foodborne Pathogens and Disease
Finishing pigs infected with Salmonella pose significant food safety risks by carrying the pathogen into abattoirs. This study was conducted to determine the dynamics of Salmonella infection in finishing pigs, and associated immunological, physiological, and behavioral alterations, by longitudinally comparing infected to noninfected pigs during 6 weeks postinfection (p.i.). Bacteriological data revealed that all inoculated pigs started shedding Salmonella within 2h 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 3–4 log10 cfu/g of Salmonella at 24h p.i., and 4–5 log10 cfu/g of Salmonella up to 4 weeks p.i. Levels of Salmonella dropped markedly (p<0.05) in all samples at 5 weeks p.i. There was no difference between groups for blood cell counts. Tumor necrosis factor-α was greater (p<0.05) in infected pigs: (1) in the mesenteric lymph nodes by 48h p.i.; (2) at 24h and 3 weeks p.i. in the ileum; and (3) in the cecum and spleen at 3 weeks p.i. Interleukin-12, interleukin-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 in ventral recumbency, 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 weeks p.i. in the gastrointestinal contents and mesenteric lymph nodes, shedding high levels of the bacteria without developing clinical symptoms, but developing an immune response throughout the intestinal tract. Moreover, subtle behavioral changes measured as postures were detected, and therefore warrant additional investigation.