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

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 2(nd), 46(th) and 84(th) 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.