Abstract
Salmonella 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 Salmonella. Salmonella 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 Salmonella load. It is unclear, however, whether live attenuated Salmonella vaccines are efficacious over the life span of a layer hen. Live attenuated Salmonella 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 VaxsafeTM STM1 aroA mutant vaccine. Birds were challenged at 18 weeks of age with Salmonella Typhimurium DT9 (MLVA 03 15 08 11 550). Feces and eggs were monitored for S. 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 S. 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 S. Typhimurium DT9. Total bacterial load in feces was quantified using qPCR. No significant difference was detected between unvaccinated and vaccinated birds after challenge.
Highlights
Foodborne salmonellosis is often epidemiologically linked with the consumption of Salmonella contaminated eggs or products containing raw or under cooked eggs (Threlfall et al, 2014)
One week after the first vaccine dose, 10 of 12 (83.3%) fecal samples collected from the rearing pen of vaccinated birds were positive for STM1
One week following the second oral dose of STM1 vaccine in drinking water, 8 of 8 (100%) samples collected from the vaccinated group were positive for STM1 vaccine
Summary
Foodborne salmonellosis is often epidemiologically linked with the consumption of Salmonella contaminated eggs or products containing raw or under cooked eggs (Threlfall et al, 2014). Salmonella contamination of eggs can occur through both vertical and horizontal mechanisms. Vertical transmission is primarily associated with Salmonella Enteritidis Enteritidis) and occurs when the bacteria infects the oviduct of a hen subsequently contaminating egg internal contents during development (Gantois et al, 2009). Vertical transmission of other serovars including Salmonella Typhimurium Typhimurium) has been documented but to a much lesser extent than S. Enteritidis (Keller et al, 1997; Okamura et al, 2001; Gast et al, 2011, 2013). Horizontal contamination occurs when an egg contacts a contaminated environment (Gantois et al, 2009)
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