Immunoprophylaxis against salmonella in commercial layer chickens

Abstract

Salmonellosis is one of the most common foodborne bacterial diseases globally. Salmonella does not commonly cause disease in poultry; however they are important reservoirs of Salmonella in the human food chain and management is critical. Attenuated or inactivated Salmonella vaccines have had variable impact upon colonisation. An aroA gene deleted attenuated live vaccine has been released in Australia, whilst an inactivated vaccine has been successfully used by an Australian poultry company for some years. The main aim of this project was to evaluate the efficacy of a Salmonella Typhimurium (ST) attenuated vaccine, alone or in combination with an inactivated multivalent autogenous vaccine that contained Salmonella Typhimurium, Salmonella Infantis, Salmonella Zanzibar and Salmonella Montevideo, administered by four delivery methods, to aid the control of Salmonella in egg layer chickens. Following vaccination, a number of the birds were challenged at four ages with one of the following field-isolated serovars: Typhimurium, Infantis or Virchow. Twenty-one days following challenge the birds were euthanized and their caeca cultured for Salmonella. Throughout the study, the birds were bled at various ages to measure seroconversion, assessed as anti-Salmonella Typhimurium antibody levels; pre and post challenge. The quantitative investigation of the challenge strain in the caecum revealed a statistically significant (p < 0.05) lower challenge strain burden in the parenteral vaccinated groups compared with the non-vaccinated control group up to an age of 22 weeks. The antibody responses varied, though the combination of the attenuated vaccine given by subcutaneous injection at 6 weeks and the inactivated vaccine given by intramuscular injection at 12 weeks of age gave the highest titres. The protective effects were demonstrated for the homologous challenge strains but not the heterologous strain. This study has shown that it is necessary to provoke a strong humoral response by vaccination, in commercial layers to reduce the contamination of eggs and egg products. The pre-lay period of layers is considered an especially important age to have control over Salmonella colonisation. Thereby, if the bird is protected, the transmission of Salmonella serovars of public health importance will be reduced, if not eliminated.