| The avian infectious bronchitis (IB) is an acute contagious disease that is caused by the infectious bronchitis virus (IBV). It often shows that the respiratory, nephritic or oviducal clinical symptoms. IBV infection on young chickens could cause 30% death or reproductive organ damage, then cause egg drop, egg quality drop. Although vaccination is one of the most effective methods to prevent IBV infection, however, a lot of IBV mutations causes numerous IBV serotypes, but the cross protection between different serotypes is poor. Therefore, to study the current IB epidemic situation, to further analyses the relationship between genotypes and serotypes of predominant strains. According to all the IBV studies to select a dominant serotype candidate strain and produce vaccines, which is the main focus of the current IB prevention route.The epidemological survey has investigated 4855 pathogenic clinical samples from 18 provinces between 2010 to 2013. It shows IBV is wildly distributed and infects all kinds of chicken. The examine positive rates were 8.1%,18.1%,15.5% and 10.9% among these 4 years respectively. The S1 gene nuclear sequences of 30 IBV isolated strains have been analysed, found that the predominant IBV strains are mainly belongs to the genotype LX4, accounted for more than 90%, inter-type homology in 93.5%-100%, but the homology with H120 strains is only 77.6%-78.5%. In addition, the cleave site amino acid sequences of epidemic strains and regular vaccine strains are different significantly.Based on the chickend species, occurred age, clinical signs etc. factors to selected 5 strains (JS101024, SD100426, JS121019, BJ100306 and HuN100427), also choose 3 widely used virus strains (H120, LDT3 and 4/91stain). Each serum type has been identified by the cross-neutralisation on tracheal organ cultures with monovalent serums. It has found that all 3 LX4 genotype strains (JS101024, SD100426 and HuN100427 strain) belong to one serum type (named as JS101024 type) which is current predominant serotype in China, and it is not as same as vaccine strains. The pathogenic research results shown that all 5 same titer pathogenic virus strains presented similar clinical symptoms, pathological diagnosis and tissue lesions. However, different virus strain induces different mortalities. For example, the SD100426 strain was able to cause 40% 28days SPF chicken death; on the other hand, the JS101024 strain did not cause any death, the antibody also were tested positive earlier 3-7 days than other strains. JS101024 strain also has high reproduction ability, the 6th passage titre could reach to 107.16EID50/0.1ml, therefore, this strain was an ideal vaccine strain candidate.Inactivated vaccines have been made by the M41 stain and 3 other candidate strains (JS 101024, SD100426 and BJ100306 strain) individually, and immunised on SPF chickens, then challenged with the pathogenic SD 110426 strain. The experiment results shown that JS 101024 strain vaccine is able to induce higher and earlier antibody by 7 days, and get 100% protection from wild IBV strain challenging. The organs, such as lung and kidneys were protect perfectly. Virus expelling days shorter than others 3-7 days. Therefore this virus strain has many great vaccine strain characters, such as the low pathogenicity and high growth ability, most importantly its serum type is same as the current predominant IBVs’. This strain vaccine is able to perfectly protect from wild virus infection, and reduce virus propagation significantly in groups. It provides good protection to the current dominant genotype and serotype epidemic IBV infections. This study provided the basis for the screening and evaluate of vaccine candidate strains of IBV epidemic viruses, and established a method to prevent IBV infections. |
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