Protective efficacy of live Salmonella gallinarum 9R vaccine in commercial layer flocks.

Salmonella enterica serovar Gallinarum (S. Gallinarum) is the causative agent of fowl typhoid, a severe systemic disease of chickens that results in high mortality. In this study we re-evaluated the ability of live S. Gallinarum 9R vaccine to protect from wild-type S. Gallinarum challenge. In laboratory trials, there was a significant difference between the vaccinated and unvaccinated control groups in mortality and the re-isolation rate of the challenge strain from the tissues (P<0.05). In field trials, efficacy of the 9R vaccine by one inoculation at the age of 18 weeks and two inoculations at the age of 6 weeks and 18 weeks was persistent throughout the duration of the study from 21 weeks old to 61 weeks old. The results from this study indicate that the protection against mortality and organ invasion in highly susceptible chickens exposed to virulent strains of S. Gallinarum may be severely limited by 9R vaccine.