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 - reported by first-named author, Lotte De Ridder and co-authors from CODA-CERVA and the University of Ghent in Belgium and published in BMC Veterinary Research - evaluated the effects of two potential control measures against the spread of Salmonella Typhimurium via a transmission experiment with 56 piglets (three to 15 weeks of age).

In the experiment, two groups were orally vaccinated with 10⁷ to 10⁸ Colony Forming Units (CFU)/2mL of a new attenuated Salmonella Typhimurium vaccine ‘Salmoporc-ΔrfaJ’ with DIVA capacities (Differentiation between Infected and Vaccinated Animals) (n = 2×16). The feed of one group was additionally supplemented with coated calcium-butyrate salt.

Two weeks after vaccination, four pigs per group were orally challenged with 10⁷CFU/2mL 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.

In both intervention groups, Ra values were lower than the positive control group although these differences were not significant.

In the combination group DIVA vaccine + coated butyrate, fewer non-challenged contact animals excreted Salmonella and fewer tissue samples were found Salmonella-positive in all pigs, than for 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.

De Ridder and co-authors concluded that both interventions showed a limited, non-significant reduction of Salmonella transmission between piglets.

They added that the interventions may have application for 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.

These interventions merit further research with larger sample sizes, to optimize their use for Salmonella programmes, added the researchers.

Reference

De Ridder L., D. Maes, J. Dewulf, F. Pasmans, F. Boyen, F. Haesebrouck, E. Méroc, S. Roels, B. Leyman, P. Butaye and Y. Van der Stede. 2013. Effect of a DIVA vaccine with and without in-feed use of coated calcium-butyrate on transmission of Salmonella Typhimurium in pigs. BMC Veterinary Research. 9:243. doi:10.1186/1746-6148-9-243

December 2013