Cultivation Of Infectious Bronchitis Virus Sczy3 Cell-adapted Strain And Its Immune Efficacy

Infectious bronchitis (IB) is an acute and highly contagious disease and caused by infectious bronchitis virus (IBV). IBV has highly variability and numerous serotypes, but little or no cross protection exists among different serotypes. The attenuated vaccine is mainly used for prevention of IB at home and abroad, but some existing traditional vaccines have not provided effective protection against the prevalent strains on the current. It’s best choice that local IBV serotypes was used for developing vaccines that provide effective protection and immune procedure.An IBV strain Sczy3 is LX4 genotype and isolated fromour laboratory in 2009. It’s hope to prepare a candidate strain of IBV attenuated vaccine that the virus was attenuated by passaging 100 times throughchicken embryo kidney cell (CEK). The experimental results showed that IBV strain Sczy3 was becomingacclimated to CEK cell and made CEK cell produce typical cytopathic such as syncytium, plaque during the passage. And it proved that strain Sczy3 has been fully weaken by passaging continuously because no clinical symptoms was observed and the morbidity and mortality were 0% when the Sczy3 C100 were inoculated.An SYBR Green I-based real-time polymerase chain reaction assay was developed in order toinvestigate the dynamic changes in IBV load in the supernatant of primary CEK cells, and the result suggested that the dynamic change curve of the IBV load in the supernatant of primary CEK cells showed a single peak and the peak of the virus load appeared at 36 h post-infection and then decreased gradually in the order of 20th> 50th>90th for the 3 generations of CEK-adapted strains.To evaluate the immune protective efficacy of Sczy3 C100 to homologous strain anddifferent genotypes,7-day-old non-immune chickens were inoculated by Sczy3 C100, 4/91 and H120 commercial vaccines, and challenged respectively by Sczy3 P3 and SCTW isolates in 2 weeks after the first and second immunization. Serum antibody detection,clinical symptoms and organ protection were used for testing the efficacy of Sczy3 CEK-adapted IBV field strains, and the preparation of histopathological setions.The results showed that all the immunized chickens showed positive serum antibody response. Sczy3 C100 could supply effective immune protection to homologous strain Sczy3 P3, which also could provide some clinical protection against non-genotype strain SCTW but high percentages of virus excretion were detected from trachea and kidney of challenged chickens. At present, numerous IBV genotypes are circulating in china, so the research on new IBV vaccine has a long way to go.