| Summary: | ABSTRACT: Salmonella enterica serovar Gallinarum biovar Gallinarum (SG) is a host-specific bacteria that causes the fowl typhoid (FT). This disease is highly pathogenic to commercial chickens, specially brown layers and breeders, causing acute septicemia followed by high morbidity and mortality. Vaccination is extensively adopted in the fields as a biosafety tool for prevention of isolated infections and outbreaks in commercial poultry flocks. The present study evaluated the use of an attenuated SG with deletions on genes cobS and cbiA (SGΔcobSΔcbiA) as a live vaccine, using vaccination schemes adjusted for field conditions. To this end, brown layers were used in two different experiments, to evaluate the long-term protection, necessary in the fields. The vaccination scheme on the first experiment consisted of two doses, the first at 4 th week-of-age and the booster dose at 8 th week-of-age with challenge at 16 th week-of-age with wild SG strain. On the second experiment, the vaccination was carried out by different routes using three doses of the live vaccine, at 4 th , 8 th and 12 th weeks-of-age, and the challenge was done at 20 th weeks-of-age. After the challenge, the mortality was recorded during 28 days, and the egg production (experiment 2) was evaluated and compared with the group of unvaccinated layers. In both experiments, the mortality was significantly reduced, and the egg production was not affected in vaccinated layer-hens. In summary, this study shows the efficacy and the protection of different vaccination schemes against FT that can be applied under field conditions in commercial poultry farms.
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