Immunogenicity and Efficacy of Live Infectious Bronchitis 793/B.08IR Vaccine in SPF Chickens

Infectious bronchitis virus (IBV) has a variety of serotypes with relatively limited cross-protection leading the disease to be a major problem in the poultry industry. The IBV 793/B strain has identified to circulate in Iran; therefore, the development of a specific vaccine to protect against the virulent virus has received attention. In this regard, the live IB 793/B vaccine (793/B.08IR) was developed in the Razi Vaccine and Serum Research Institute. In this study, the immunogenicity of 793/B.08IR vaccine via different routes of vaccination and efficacy of the vaccine were determined in specific-pathogen-free (SPF) chickens. Three treatment groups of 10 SPF chickens received the vaccine via eye drops, spray, and drinking water. The sera were collected from the chicks at 3 and 6 weeks after the vaccination, and IBV specific antibody was measured using enzyme-linked immunosorbent assay (ELISA) and serum neutralization (SN) test. To evaluate 793/B.08IR vaccine efficacy, 10 SPF chickens were vaccinated using eye drops. Moreover, 10 unvaccinated chickens were separately retained as negative controls. The birds were challenged with the virulent virus 3 weeks following the vaccination. Five days after the challenge, the tracheal swab was taken for virus reisolation. In the immunogenicity test, the ELISA titers of three vaccinated groups were significantly higher than the background values obtained in the control group (p<0.0001). The mean value of ELISA titer in the spray vaccinated group was higher than the spray and drinking water vaccinated groups 3 weeks following the vaccination; however, the difference was not statistically significant. No differences were observed in antibody titers among the three vaccinated groups 6 weeks after the vaccination. The results of the SN test confirmed the data obtained from the ELISA. The results of antibody titer and its increasing trend in chickens showed that 793/B.08IR vaccine induce proper immunity against the virus. In the efficacy test, IBV was isolated from 90% of the unvaccinated controls and 10% of vaccinated groups. The results of the recovery of the virus after the challenge showed that 793/B.08IR vaccine can provide a significantly improved protection against the pathogen in SPF vaccinated chickens.