Protection of chickens against fowl typhoid using field vaccine programs formulated with the live attenuated strain Salmonella Gallinarum ΔcobSΔcbiA

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.摘要：鸡沙门氏菌血清型鸡亚种（Salmonella enterica serovar Gallinarum biovar Gallinarum，SG）是一种宿主特异性细菌，可引发鸡伤寒（fowl typhoid，FT）。该病原菌对商品禽群（尤其是褐壳蛋鸡及其种鸡）具有极强致病性，可引发急性败血症，伴随高发病率与高死亡率。疫苗接种作为生物安全防控手段，已在畜禽养殖领域广泛应用，用于预防商品禽群的散发性感染与暴发疫情。本研究采用适配田间实际养殖条件的免疫程序，评估cobS与cbiA基因缺失的减毒SG菌株（SGΔcobSΔcbiA）作为活疫苗的应用效果。为此，本研究开展两项不同实验以评估田间养殖所需的长期免疫保护效果，实验对象均为褐壳蛋鸡。第一项实验采用两剂免疫程序：首剂于4周龄接种，加强剂于8周龄接种，并于16周龄用野生型SG菌株进行攻毒。第二项实验则采用不同接种途径，于4、8、12周龄分三剂接种该活疫苗，并于20周龄开展攻毒试验。攻毒后连续28天记录死亡率，并对第二项实验的产蛋性能进行评估，同时与未免疫的褐壳蛋鸡组进行对比。两项实验结果均显示，免疫组蛋鸡的死亡率显著降低，且产蛋性能未受影响。综上，本研究证实了适配商品禽场田间养殖条件的多种免疫程序，可有效防控鸡伤寒并提供可靠免疫保护。