Comparison Immunogenicity Of Different Attenuated Vaccine To IBV

Infectious bronchitis (IB) caused by infectious bronchitis virus (IBV) is a highly acute and contact disease, which is one of the diseases damaging the development of poultry husbandry in the world and result in enormous economic loss. To investigate the protective effect of the current commercial attenuated IB vaccines to the epidemic IBV strains in Sichuan and provide some references for selecting fitable vaccines against the virulent IBV, the paper compare the protective effect of three attenuated IB vaccines (H120, W93and4/91) through challenging chicks with two representative virulent IBV in Sichuan.Lung and kidney tissue were collected from sick chicken and were used to isolate IBV strains by passaging in non-specific immune chicken embryo. And then, the isolates were identified through the method of HA and RT-PCR and the experiment of causing the chicken embryo dwarf. A IBV strain was isolated and designated as SCTW. The S1gene of SCTW was cloned and sequenced, and then was alignment with the other27representative IBV strains from GenBank. The result demonstrated that SCTW was a TWⅠ genotype strain firstly isolated in Sichuan and had high nucleotide homology (90.4%,89.8%,89.5%and88%, respectively) and amino acid homology (91.7%,90.7%,90.2%and88%, repectively) with TW2575/98,3051/02,3071/03and3376/06, which confirmed that amino acid residues possess difference and the mutated region mainly located on the latter segment of S1gene. After confirming genotype, the pathogenicity of SCTW was investigated based on morbidity, mortality and histopathology of exiperiment chicks challenged with SCTW at15d. The result showed that there were100%morbidity and40%mortality on infected chicks, and besides SCTW strain cause severe tissue damage of respiratory tract and kidney, indicating SCTW has high pathogenicity.White feather broilers that were immunized with three different vaccines were challenged by artificial infection with SCTW and ZY3stored in our lab. The antibody titre was detected by the method of ELISA before and after immunizing, and the result showed that the level of antibody and the beginning time of producing antibody were similar among three different vaccines. The morbidity, morbility, postmortem and histopathology of each group were observed, and then the virus were detected by the method of RT-PCR from the lung, kidney and respiratory tract of each group. The result of morbidity and morbility demonstrated that protection rate of4/91reached above70%, and higher than the other two vaccines. The4/91vaccine had the best efficiency among the three vaccines, and the kidney protection rate of4/91was higher than W93by13%and the lung protection rate higher than both W93and H120by30%. Meanwhile, the RT-PCR dectection rate of virus in chicken immunized with4/91was the lowest among the three strains, which further indicated that the protective efficiency of4/91for chicken was better than both W93and H120.All result demonstrated that the protective efficacy of4/91is bitter than W93and H120and4/91vaccine is more fitable attenuated vaccine in current vaccines. Howerver, the immunized efficiency don’t reach the standard according to different evaluation standards on the immunized effect of vaccine, so it is still difficult to prevent IB and it’s significant to research new IB vaccines.