Efficacy of a novel virulence gene-deleted Salmonella Typhimurium vaccine for protection against Salmonella infections in growing piglets.
ABSTRACT We have previously developed a novel attenuated Salmonella Typhimurium (S. Typhimurium) ΔcpxR Δlon vaccine. This study was carried out to examine whether this vaccine could effectively protect growing piglets against Salmonella infection. Attenuated S. Typhimurium secreting the B subunit of Escherichia coli heat-labile enterotoxin was also used as a mucosal adjuvant. Pregnant sows in groups A and B were primed and boosted with the vaccine and mucosal adjuvant, whereas sows in groups C, D and E received PBS. Piglets in groups A and C were intramuscularly primed with formalin-inactivated vaccine and orally boosted with live vaccine, while piglets in groups B, D and E received PBS. Piglets in groups A, B, C, and D were challenged with a wild type virulent S. Typhimurium at the 11th weeks of age. Colostrum sIgA and IgG titers in vaccinated groups A and B sows were approximately 50 and 40 times higher than those of non-vaccinated groups C, D and E sows (P<0.001). Serum IgG titers of group A piglets were also significantly higher than those of groups D and E piglets during the study (P<0.001). Furthermore, no clinical signs were observed in group A piglets during the entire experimental period after the challenge, while diarrhea was observed in many of the piglets in groups B, C, and D. No Salmonella was isolated from fecal samples of the groups A and C piglets on day 14 after challenge, whereas the challenge strain was isolated from several piglets in groups B and D. These results indicate that vaccination of the piglets with the vaccine and mucosal adjuvant in addition to vaccination of their sows induced effective protection against Salmonella infections in the growing piglets.
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ABSTRACT: Reducing zoonotic pathogens in food animals prior to harvest will reduce the pathogen burden that enters the food chain and the environment. Consequently, the burden of enteric illness in humans may be reduced. Evaluating interventions to reduce a pathogen in animals often begins with challenge trials, in which animals are deliberately exposed to the pathogen under controlled conditions. Challenge trials are subsequently followed by field trials, also known as randomized controlled trials, in which the animals are naturally exposed to the pathogen. Challenge trials can most effectively inform field trials only if they precede field trials, are robust, internally valid and transparently reported. Using systematic review and meta-analysis methodology, we examined the pre-harvest food safety literature for three intervention-pathogen-species combinations: probiotics/competitive exclusion products in ruminants to reduce Escherichia coli O157 shedding, vaccines in ruminants to reduce E. coli O157 shedding and vaccines in swine to reduce Salmonella shedding. We examined two outcomes, prevalence of faecal shedding at the end of the trial and prevalence of faecal shedding throughout the trial period, to compare challenge trials and field trials. We found that challenge trials occurred concurrently with field trials, challenge trials suffered from reporting deficiencies of methodological features, challenge trials tended to report a more favourable outcome than field trials, and there was some evidence of publication bias among all three intervention-pathogen-species combinations. Challenge trials would better serve to inform field trials if they precede field trials, are methodologically sound, include transparent reporting and are published regardless of their results. In addition, due to our findings of greater efficacy reported among challenge trials compared with field trials, risk models predicting the public health benefits of pre-harvest interventions to reduce zoonotic pathogens in livestock might be best served by field trial results alone.Zoonoses and Public Health 11/2013; · 2.09 Impact Factor
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ABSTRACT: Despite current control measures, Salmonella in pigs remains a major public health concern. In this in vivo study, the effect of three intervention strategies on Salmonella Typhimurium transmission in pigs was evaluated. The first intervention was feed supplemented with coated calcium-butyrate (group A); the second comprised oral vaccination with a double-attenuated Salmonella Typhimurium strain (group B), and the third was acidification of drinking water with a mixture of organic acids (group C). After challenge at 8weeks of age, animals were individually sampled for 6weeks (blood once per week; faeces twice per week) and then were euthanased at 14weeks of age. Post-mortem ileum, caecum, ileocaecal lymph nodes, and tonsils were sampled, along with ileal, caecal and rectal contents, and tested for the presence of Salmonella spp. Transmission was quantified by calculating an 'adjusted' reproduction ratio 'Ra' and its 95% confidence interval (CI). The proportion of pigs that excreted Salmonella spp. via the faeces was significantly higher in group C (58%, P<0.0001) and the positive control group (41%, P=0.03), compared to group B (15%), and the proportion in group C was also significantly higher than in group A (23%, P=0.01). Group A had the lowest proportion of positive post-mortem samples (18%), followed by group B (31%), the positive control group (41%) and group C (64%) (P<0.03). The highest transmission was seen in the positive control group and group C (Ra=+∞ with 95% CI [1.88; +∞]), followed by group B (Ra=2.61 [1.21; 9.45]) and A (Ra=1.76 [1.02; 9.01]). The results of this study suggest that vaccination and supplementation of the feed with coated calcium-butyrate limited Salmonella transmission in pigs and might be useful control measures.The Veterinary Journal 05/2013; · 2.42 Impact Factor
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ABSTRACT: Text 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-[increment]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. 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) ELISAs 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. 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.BMC Veterinary Research 12/2013; 9(1):243. · 1.86 Impact Factor