The entire S1 protein genes of eight infectious bronchitis (IB) vaccine strains used in China were compared with those of the IB virus isolates present in the field in China. The nucleotide and amino acid similarities between the eight IB vaccine strains and the field strain, tl/CH/LDT3/03, which was isolated from a teal (Anas sp.), were not more than 81.1% and 79.2%, respectively. Phylogenetic analysis based on the S1 genes showed that the vaccines and field strains belonged to different clusters and showed larger evolutionary distances, and indicated that they were of different genotypes. Four out of the eight vaccines, in addition to the Massachusetts type vaccine H120, were used for protection tests against challenge by the IB virus isolate tl/CH/LDT3/03. This revealed that each of the five IB vaccines induced poor protection against the teal isolate, as assessed by respiratory protection, clinical signs and mortality, indicating the necessity of developing vaccines from local strains for IB control in China.
Avian infectious bronchitis virus (IBV) causes tremendous economic losses to the poultry industry worldwide. Different serotypes of this virus show little cross-protection. The present study investigated the genotypic relationship between CK/CH/LDL/97I-type strains and reference IBVs based on S1 gene comparisons and the protection provided by vaccination with commercial vaccines and attenuated homologous and heterologous strains. Phylogenetic analysis and the comparison of S1 showed that CK/CH/LDL/97I-type virus might be a new serotype compared to vaccine strains and other types of IBV isolates in China. Protection efficacy was evaluated by morbidity, mortality, and virus re-isolation from the challenged chicks. Complete protection by IBV vaccination was provided by the homologous strain but sufficient respiratory protection was not provided by the commercial vaccines. Heterologous strains against CK/CH/LDL/97I challenge and the development of a vaccine against CK/CH/LDL/97I-type IBV will be necessary to control infectious bronchitis disease in poultry. Further development of the attenuated CK/CH/LDL/97I strain may provide a valuable contribution towards this goal.
Seventy-eight isolates of avian infectious bronchitis virus (IBV) were obtained from different field outbreaks in China in 2009 and genotyped with 34 reference strains. Four genotypes of IBV and three new isolates were identified by phylogenetic analysis and BLAST searches of the entire S1 gene. The results showed that most IBV strains that have circulated in China in recent years belong to the genotype of QX-like strains, and that they could be grouped further into two clusters, regardless of the level of genetic variation displayed. A study of pathogenicity that used three QX-like strains*ck/CH/LSD/091003, ck/CH/LDL/091022 and ck/CH/LJL/ 090330*showed that the isolates caused the most severe lesions in the kidneys and were therefore nephropathogenic strains with various levels of virulence in specific pathogen free chickens. A vaccinationÁ challenge test that was performed using the three QX-like strains showed that the commercially available H120 vaccine did not provide sufficient protection against challenge with the QX-like isolates, as demonstrated by comparison of the clinical signs, pathological lesions and virus recovery from the trachea and kidney of unvaccinatedÁchallenged and vaccinatedÁchallenged birds.
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