Live and inactivated vaccine regimens against caecal Salmonella Typhimurium colonisation in laying hens

Abstract

Objective: In Australia, Salmonella serovar Typhimurium (S. Typhimurium) is the predominant zoonotic serovar in humans and is frequently isolated from layer hens. Vaccination against this serovar has been previously shown to be effective in broilers and the aim of this current study was to assess and determine the best vaccination strategy (live or inactivated) to minimise caecal colonisation by S. Typhimurium.

Methods: A long-term experiment (56 weeks) was conducted on ISABROWN pullets using a commercial live aroA deleted mutant S. Typhimurium vaccine and an autogenous inactivated multivalent Salmonella vaccine (containing serovars Typhimurium, Infantis, Montevideo and Zanzibar). These vaccines were administered PO or by SC or IM injection, either alone or in combination. Pullets were vaccinated throughout rearing (to 18 weeks of age) and sequentially bled for antibody titre levels. The birds, vaccinated and controls, were challenged orally with a field isolate of S. Typhimurium at different ages, held for 21 days post-challenge, then euthanased and their caeca cultured for the presence of Salmonella.

Results: None of the oral live-vaccinated groups exhibited lasting protection. When administered twice, the inactivated vaccine gave significant protection at 17 weeks of age and the live vaccine given by SC injection given twice produced significant protection at 17, 25 and 34 weeks.

Conclusions: Vaccination regimens that included parenteral administration of live or inactivated vaccines and thus achieved positive serum antibody levels were able to provide protection against challenge. Hence, vaccination may play a useful role in a management strategy for Salmonella carriage in layer flocks.

Keywords: Salmonella Typhimurium; layer chickens; poultry; vaccines.

Figure 1

Mean log₁₀ Salmonella Typhimurium antibody ELISA titres in non‐challenged birds by vaccination groups over time. (A) Groups that received only an oral dose of the live vaccine (Vaxsafe® ST: Strain STM‐1, Bioproperties Pty Ltd, VIC, Aust; live‐attenuated aroA deletion mutant of S. Typhimurium). (B) Groups that received the inactivated vaccine (containing field isolates of serovar S. Typhimurium, Infantis, Montevideo and Zanzibar at 10⁸ CFU of each serovar per bird dose) by IM injection only at 12 weeks of age. (C) Groups that received the inactivated vaccine at 6 and 12 weeks of age or live vaccine by SC injection at 4 and 8 weeks of age. All charts show unvaccinated birds as a reference point and the x‐OvO ELISA positive cut‐off point (log₁₀ 2.89). Bars show standard error. CFU, colony‐forming units.