Demonstration of the efficacy of a Salmonella Enteritidis live vaccine for chickens according to the current European Pharmacopoeia Monograph

Abstract

Since 2013 the efficacy of new live Salmonella Enteritidis (SE) vaccines for chickens needs to be demonstrated according to European Pharmacopoeia Monograph 04/2013:2520 to receive approval in the EU. The purpose of this study was to determine whether a vaccine licensed since 1999 could also fulfil the required tests of the current guideline. For this, Salmonella-free chickens (n = 50) were vaccinated on their 2nd, 46th and 84th day of life with the live attenuated S. Enteritidis strain IDT No. 441/014. Non-vaccinated control animals (n = 50) were kept accordingly. To demonstrate the duration of immunity 20 animals of each group were challenge infected 65 weeks after the last vaccination with a virulent SE (PT 4) strain. According to the monograph, cloacal swabs were taken 3, 5, 7, 10 and 14 days post challenge (dpc). Tissue samples of liver, spleen, caeca, ovaries and oviduct were collected during necropsy of 10 animals per group on 7 and 14 dpc, respectively. All samples were analysed bacteriologically regarding the presence of the challenge strain. The number of challenge strain positive tissue samples and cloacal swabs was significantly reduced in vaccinated animals (p < 0.05). Therefore, the vaccine strain complied with the EP guideline. This study is the first that demonstrates the efficacy of this vaccine according to the current regulations. However, efficacy could also be shown during the development of the vaccine but by use of another animal model that comprised fewer animals per group. The use of this model is no longer accepted by EU regulatory authorities. The results need discussion in context with the 3R principle.

Invasion inhibition effects and immunogenicity after vaccination of SPF chicks with a Salmonella Enteritidis live vaccine

“…However, they could not show a significantly reduced excretion of the challenge strains, measured by the number of Salmonella positive cloacal swabs, independently from the different vaccination regimen. This contrasts with the results of Theuß et al [10], showing a significant and relevant reduction of the number of positive cloacal swabs after threefold vaccination with a SE-LV.…”

“…Thus it can be assumed that the Salmonella group D specific antibodies detected are antibodies against S. Enteritidis. The increase of the specific antibody titers after vaccination with the SE-LV and subsequent challenge with virulent S. Enteritidis strains corresponds to reports from Methner [7], Springer et al [9] and Theuß et al [10]. The increase after vaccination is usually much lower than after infection.…”

“…The evidence of an adaptive immune response against S. Enteritidis PT4 after vaccination with a SE-LV (Salmovac SE, Salmovac 440, both Ceva Santé Animale, Libourne, France) was demonstrated with quantitative challenge models by Martin et al [17], Springer et al [9][18], Atterbury et al [19] and Methner [7]. Furthermore, Theuß et al [10] showed the efficacy of the vaccine after challenge with a S. Enteritidis PT4 strain according to the qualitative method described in the European Pharmacopoeia monograph 04/2013:2520.…”

“…Braukmann et al [5] were the first to show inhibition of the systemic invasion of a virulent S. Enteritidis strain (innate immunity) just 2 days after vaccination with a commercially available attenuated S. Enteritidis live vaccine (SE-LV). In contrast, the occurrence of an adaptive immune response has been shown several times for different vaccines by different authors [6][7][8] [9] [10].…”

Safety of bivalent live attenuated Salmonella vaccine and its protection against bacterial shedding and tissue invasion in layers challenged with Salmonella

“…Long persistence in tissues was conceived to induce protective immune responses by live attenuated vaccines. The negative results for Salmonella revealed that these vaccine strains could not colonize and invade livers, spleen, ovaries, and oviducts, which the wild type of Salmonella most frequently targeted ( Theuß et al., 2018 ). The stimuli of vaccine stains may have been sufficient for well-established adaptive immunity before the time of visceral sample collections (week 25).…”