Preliminary Analysis of the Duration of Protection of Vaxsafe St Vaccine against Salmonella Shedding in Layers

Vaxsafe ST (Bioproperties Pty Ltd) is an aroA deletion mutant vaccine for the control of Salmonella Typhimurium in chickens. It is registered for spray and drinking water applications and has been shown to aid in the control of Salmonella in short lived birds (such as broilers). The main objective of this study was to test efficacy of Vaxsafe ST with a new vaccination program aimed at lengthening the duration of immunity for the full productive life of layers. The first dose was delivered by spray on chicks at one day of age followed by two doses administered orally at 2 and 6 weeks of age (woa) respectively, and a fourth dose administered by intramuscular (IM) injection at 10 woa. All vaccination doses were administered at 10 cfu/dose. For the fourth IM dose, the vaccine was delivered in two different formats, mixed in diluent or in a mixture with Nobilis EDS+ND vaccine (Intervet). At 16, 30, 45 and 65 woa respectively (that is at 6, 20, 35 and 55 weeks post IM vaccination) a sample of the vaccinated birds, was transported to a research facility and challenged with wild type S. Typhimurium (ST) or S. Infantis (SI). Salmonella shedding of vaccinated birds were compared with a control unvaccinated (challenged) group in order to assess efficacy of the vaccine. Vaxsafe ST delivered in either diluent or with Nobilis® EDS+ND killed vaccine, provided protection against strong homologous (ST) and heterologous (SI) challenges compared to the unvaccinated birds.