Preparation Of The Attenuated Live QX-like Infectious Bronchitis Virus Strain And Its Preliminary Evaluation Of The Safety And Efficacy

Avian infectious bronchitis(IB) is an acute and highly contagious disease caused by the avian infectious virus(IBV). Attenuated vaccine is used for this disease, but the common universal vaccine can not provide effective immune protection, so it is necessary to develop vaccines from local IBV strains of this serotype.In this study, SDZB0808 strain was isolated from commercial broiler of Shandong province. In our previous studies, the whole sequences of SDZB0808 were sequenced, and the genetic evolution analysis showed that the strain was a major epidemic strain in our country.The cross neutralization tests showed that the strain antigens spectrum is broad, Cross neutralization reaction antigen of the experimental results show that the strain is broad and the antibodies could be reacted with other serotype antigens. This strain can be used as a vaccine candidate strain. Then SDZB0808 strain was passaged in SPF chicken embryo. The attenuate of different passage were studied, the P100 and P110 have a good effect on protection.Regarded SDZB0808 as the reference strain, a total of 30 nucleotides were deleted in the genome(3244-3273) of P100 which resulted in 10 amino acids deletion in the ORF 1a(906-915) from P62. Because P1 and P100 were different in the genome, specific primers were designed. No amino acid genome named QD genome, lack of amino acid genome for RD genome, and SYBR Green I Real-Time fluorescence quantitative detection method for quantitative analysis was performed to P60, P100 and P110. The result showed that: two kinds of genome have different proportion in P60, P100, P110. The relative values showed a downward trend. The results showed that the mutations and deletions in the genome may have resulted in the attenuation of SDZB0808. We can conclude that attenuated infectious bronchitis virus may be due to the orientated selective of the SPF embryonated chicken eggs to the attenuated. The mechanisms of attenuation still be needed further researched.P100 were evaluated in 3-day-old specific pathogen free(SPF) chickens which possiblely be used as a live IBV vaccine strain. In the safety test, clinical signs, pathological changes and histopathologic lesions were not observed in chickens inoculated with P100 at a dose of 105.5EID50. In the vaccination-challenge test, 3-day-old chickens were vaccinated with P100 at a dose of 104.5EID50 and challenged with homologous IBV strain SDZB0808 andheterogenous strain SDIB821/2012 at a dose of 106.0EID50 at 17-day-old age, respectively.Based on clinical signs and the death rate of chickens after viral challenge, P100 can produce100% protection chickens against SDZB0808 and SDIB821/2012, respectively. P100 also showed that there was no reversion about virulence after five back passages in chickens. The result of RT-PCR was positive, the SPF chiken embryo were pathology.The results preliminary indicated that P100 was safe and efficacious as a candidate vaccine against QX-like IBV strains.