Research On The Antigen Correlation And Pathogenicity Of QX Avian Infectious Bronchitis Virus

Infectious bronchitis(Infectious bronchitis IB)is an acute and highly contagious respiratory infectious disease.The disease has been widely popular in the world and became one of the diseases that brought serious harm to the global development of poultry industry.At present,the main measure to prevent and control the disease is vaccination.However,IBV is constantly evolving leading to the occurrence of new genotypes and serotypes.If the vaccine used is antigenicly different from epidemic field strain,immune failure may occurred.So continuous detection of the IBV and timely understanding of the trend of IBV genetic variation,antigen characteristics,pathogenicity and so on will give valuable reference for the prevention and control of IB.This paper planed to make a molecular epidemiological research of IBVstrains(IBVs)epidemic in Sichuan area during2015-2015 firstly,then studied the difference of antigenicity and pathogenicity of IBV strains in the QX genotype.In this study,23 strains of IBV were isolated and identified in parts of Sichuan area during 2015-2017.The S1 gene was cloned and sequenced,and phylogenic tree was constructed by comparing the S1 gene of IBVs.The result showed that 23 IBV isolates could be clustered into 5 genotypes which are QX type,4/91 type,Mass type,TW? type,and TC07-2 type.The QX genotype IBV is the dominant strains in Sichuan province in recent years,accounting for 65% of isolates.Two TC07-2 type strains were also isolated and that were the first existence of TC07-2 type IBVs in Sichuan province.Three of the 23 strains were recombinant strains and the recombination mainly occurred between QX-type and TW I –type,and QX type and 99 I type.To research the antigenicity of the same genotype,eight QX-type strains were selected,and reciprocal neutralizing test showed that there were difference in the antigenicity among eight QX-type isolates and antigen Map analysis showed that they can be divided into three antigen groups,and there were also small differences between the isolates of the same antigen group.The IBVs from the same genotype have difference in antigenicity.Six strains of QX-type were chose to study the pathogenicity and the results showed that QX-type IBVs were all pathogenic to chickens,but there were difference in pathogenicity between different QX type IBVs.The isolates A/CH/DYW16 and A/CH/ms17 had the strongest pathogenicity than other isolates and the mortality reached 50% and 30%,respectively.Clinical anatomic observation showed that the peak point of clinical symptoms varied between different strains.The virus load detection results showed that the dynamic changes of virus load varied between different IBVs,and had no correlation with the dynamic changes of clinical signs.