Serotype Identification And Immunogenicity Of Guangxi Isolates Of Avian Infectious Bronchitis Virus

Infectious bronchitis (IB) is one of the highly contagious respiratory and acute diseases in chickens caused by infectious bronchitis virus (IBV). Since the serotypes of IBV are numerous, there are differences of cross-protective effect between different serotypes. Extremely great economic losses around the world poultry industry due to the vaccination failure have been resulting from the difference of serotypes between the epidemic strains and vaccine strains. Therefore, it is important and essential to identify the serotypes of local IBV epidemic isolates and screening ideal strain as a candidate for development of suitable vaccine by testing of immunogenicity and cross immunity protection.Firstly, on the base of our topic had been divided in to seven serotypes of26IBV isolates during the years of1985to2008, six different serotypes were chosen to identify the serotypes of20Guangxi IBV isolates from2009to2011on tracheal organ culture VN tests. The results showed that six serotypes were still vested of all20strains. Six isolates including GX-YL0902, GX-NN1009, GX-NN1013, GX-YL1019, GX-NN110034and GX-NN-4belong to serotype1; Four isolates including GX-NN1012, GX-GL2, GD-KP1033and GX-NN-14 belong to serotype2; Five strains including GX-NN1014, GX-NN1011, GX-NN09093, GX-NN110033and GX-NN-11belong to serotype3; isolate GX-GL1belongs to serotype4; two isolates GX-HC1006and GX-NN09032belong to serotype5; two isolates GX-YL1121and GX-NN-13belong to serotype6.Secondly,4isolates included GX-YL5, GX-YL9, GX-NN7, GX-C represented different genotypes and serotypes and1vaccine strains HI20which were widely used in the industry, were used to run immunogenicity and cross-protective immunity test according to the immune efficacy test of the national IBV inactivated vaccine. All the chickens were immuned with inactivated oil emulsion vaccine (OEV) of various strains subcutaneously at14days, and21d after immunization were challenged the isolates by intranasal and eye-The clinical morbidity and mortality, dynamic changes on antibody levels and virus recovery of respiratory system (trachea and lung) and urinary system (kidney) were evaluated respectively. The findings showed that it caused mild clinical symptoms in vaccined birds, the morbidity and mortality rate were0to10%and0-20%respectively,difference between groups was not significant (p>0.05); un-infected control birds had a very significant difference (p<0.01) or significant difference (p<0.05) with vaccined birds, which performed more serious clinical symptoms and morbidity and mortality rate were40%to70%and20%to40%, respectively. The antibody response detected by indirect ELISA before and after7d,14d and21d immunizations. The vaccine to produce antibodies after7d, with the exception of the GX-NN7group antibody levels showed a slight decline in time, the rest had time-varying linear upward trend. Eighty percent of serum samples were positive after2Id immunization. However, control group antibody levels were always negative. Re-isolation viruses were taken to test from trachea, lung and kidney of vaccinated chickens after5d challenging, the results showed that virus detection rate was0to40%, corresponding the protection rate was60%to100%in immuned groups. There was no significant difference among the immuned groups (p>0.05), but had significant difference compared with un-infected groups (p<0.01);The virus detection rates of H120against GX-C, GX-NN7, GX-YL5, GX-YL9were10%,20%,30%,30%respectively, it indicated that commonly used vaccine viruses can’t provide full protection against the field isolates. The other four OEV vaccines can provide good protection (60%-100%) against the challenges with homogenous and heterogeneous viruses, the protections of OEV of GX-YL9against isolates GX-YL9, GX-C, GX-NN7, GX-YL5were the best by100%,90%,70%and100%respectively, which may be a good candidate strain for the prevention and control of the local IBV.The results of study demonstrated that the serotypes of IBV in Guangxi were complicated. H120can’t provide full protection against the epidemic isolates, and screen good immunogenicity strain for development of multivalent OEV is an effective strategy for prevention and control of IBV in Guangxi.