Safety and protective effects of an avirulent Salmonella Gallinarum isolate as a vaccine candidate against Salmonella Gallinarum infections in young chickens.

ABSTRACT

Fowl typhoid is an important disease of chickens and turkeys, which is caused by Salmonella Gallinarum (S. Gallinarum). Vaccines with high levels of protective effects against fowl typhoid need to be developed for the poultry industry. In this study, a S. Gallinarum strain, named SG01, was isolated from a poultry farm in Mashan region of Wuxi City, China, and identified through biochemical tests and specific PCR amplifications. Then, safety evaluations of the SG01 strain were performed in young chickens. No clinical symptom including depression and diarrhea and gross lesion involved in the cardiac nodule, hepatic necrotic lesion and splenic necrotic lesion, was determined on fifteen-day-old chickens after immunization with 1 × 1010 CFU of the SG01 strain through the oral route. However, diarrhea symptoms and hepatic lesions were identified from chickens immunized with the commercial vaccine strain SG9R by the same dose and route. At 14 days post inoculation, SG01 strain was eliminated in the liver and spleen from SG01-immunized chickens, while the SG9R strain still could be identified from SG9R-immunized chickens. After challenge with the virulent S. Gallinarum strain, significant reduction of the morbidity rate was found in the SG01 immunized group (20 %) compared to the challenge group (100 %) according to signs scoring systems for clinical symptoms and gross lesions. Additionally, immunization with the SG01 strain could provide more than 8 weeks of protection periods against fowl typhoid. These results demonstrate the SG01 strain is avirulent to young chickens and might be safer compared to the SG9R strain. In addition, SG01 strain is a potential vaccine candidate against fowl typhoid in young chickens.