title: Effect of a DIVA vaccine with and without in-feed use of coated calcium-butyrate on transmission of Salmonella Typhimurium in pigs.
abstract: BACKGROUND
  For satisfactory Salmonella control, good biosecurity along the pork production chain is crucial, although additional control measures on-farm need to be considered. This study evaluated the effect of two potential control measures against the spread of Salmonella Typhimurium via a transmission experiment with 56 piglets (3-15 weeks of age): two groups were orally vaccinated with 107 - 108 Colony Forming Units (CFU)/2 mL of a new attenuated Salmonella Typhimurium vaccine 'Salmoporc-∆rfaJ' with DIVA capacities (Differentiation between Infected and Vaccinated Animals) (n = 2x16); the feed of one group was additionally supplemented with coated calcium-butyrate salt. Two weeks post vaccination, four pigs per group were orally challenged with 107 CFU/2 mL of a Salmonella Typhimurium strain 112910a. Both groups were compared with a positive (challenged/untreated; n = 16) and negative (unchallenged/untreated; n = 8) control group. Until six weeks post challenge, blood, individual faecal and finally tissue samples were examined. Adjusted transmission ratios 'Ra' were estimated, based on the challenge strain isolation from faecal and/or tissue samples.
  
  
  RESULTS
  In both intervention groups, Ra values were lower compared to the positive control group, although these differences were not significant. In the combination group DIVA vaccine + coated butyrate, less non-challenged contact animals excreted Salmonella and less tissue samples were found Salmonella-positive in all pigs, when compared to the positive control group (P < 0.01). Seroconversion was detected in none of the vaccinated animals before challenge, when using a commercial lipopolysaccharide (LPS) ELISA targeting only Salmonella O-antigens, deleted in this vaccine. This was in contrast with an in-house whole-cell ELISA testing for various Salmonella antigens, in which Salmonella-specific antibodies were found pre-challenge in the serum of the vaccinated pigs.
  
  
  CONCLUSIONS
  Both interventions showed a limited, non-significant reduction of Salmonella transmission between piglets. They may have applications towards Salmonella control and surveillance. Firstly, the number of Salmonella excreting contact pigs was significantly lower in the group where vaccination was combined with coated calcium-butyrate salt in the feed; secondly, the new vaccine confirmed its DIVA capacity. Therefore, these interventions merit further research with larger sample sizes, to optimize their use for Salmonella programmes.
authors.affiliation: Unit of Co-ordination in Veterinary Diagnostics-Epidemiology and Risk Analysis, CODA-CERVA, Groeselenberg 99, 1180 Ukkel, Belgium. lotte.deridder@ugent.be.
authors.forename: Lotte
authors.initials: L
authors.lastname: De Ridder
authors.forename: Dominiek
authors.initials: D
authors.lastname: Maes
authors.forename: Jeroen
authors.initials: J
authors.lastname: Dewulf
authors.forename: Frank
authors.initials: F
authors.lastname: Pasmans
authors.forename: Filip
authors.initials: F
authors.lastname: Boyen
authors.forename: Freddy
authors.initials: F
authors.lastname: Haesebrouck
authors.forename: Estelle
authors.initials: E
authors.lastname: Méroc
authors.forename: Stefan
authors.initials: S
authors.lastname: Roels
authors.forename: Bregje
authors.initials: B
authors.lastname: Leyman
authors.forename: Patrick
authors.initials: P
authors.lastname: Butaye
authors.forename: Yves
authors.initials: Y
authors.lastname: Van der Stede
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002087:Butyrates / Q000627:therapeutic use*; D002118:Calcium / Q000627:therapeutic use; D019587:Dietary Supplements; D004797:Enzyme-Linked Immunosorbent Assay / Q000662:veterinary; D005243:Feces / Q000382:microbiology; D012481:Salmonella Infections, Animal / Q000517:prevention & control* / Q000635:transmission; D022562:Salmonella Vaccines / Q000008:administration & dosage / Q000627:therapeutic use*; D012486:Salmonella typhimurium; D013552:Swine; D013553:Swine Diseases / Q000382:microbiology / Q000517:prevention & control* / Q000635:transmission
chemical_list: D002087:Butyrates; D022562:Salmonella Vaccines; D002118:Calcium