A Long-Term Efficacy Trial of a Live, Attenuated <italic>Salmonella</italic> Typhimurium Vaccine in Layer Hens.

<italic>Salmonella</italic> remains one of the most common causes of bacterial foodborne gastrointestinal disease in humans. Raw eggs or food items containing undercooked eggs are frequently identified as the source of <italic>Salmonella. Salmonella</italic> Typhimurium contamination of table eggs most commonly occurs when they are laid in a contaminated environment. Several control strategies, including vaccination, are widely used to mitigate the total <italic>Salmonella</italic> load. It is unclear, however, whether live attenuated <italic>Salmonella</italic> vaccines are efficacious over the life span of a layer hen. Live attenuated <italic>Salmonella</italic> vaccines have been favored due to their ability to illicit a strong humoral immune response. The lifespan of a layer hen ranges between 60 and 80 weeks and the long term efficacy of attenuated vaccine strains has not been investigated. In this study, commercial brown layer chicks were vaccinated at day old, 6 weeks of age, and again at 10 weeks of age with the Bioproperties Vaxsafe^TM STM1 <italic>aroA</italic> mutant vaccine. Birds were challenged at 18 weeks of age with <italic>Salmonella</italic> Typhimurium DT9 (MLVA 03 15 08 11 550). Feces and eggs were monitored for <italic>S.</italic> Typhimurium for 40 weeks post-infection. Birds produced a strong immune response following the final dose which was administered intramuscularly. The serum antibody response to <italic>S.</italic> Typhimurium DT9 infection did not differ between challenged groups. Fecal shedding and egg contamination was highly variable and did not differ significantly between vaccinated and unvaccinated birds that had been challenged with <italic>S.</italic> Typhimurium DT9. Total bacterial load in feces was quantified using qPCR. No significant difference was detected between unvaccinated and vaccinated birds after challenge. [ABSTRACT FROM AUTHOR]