Screening Of Dominant Strains From Five Local IBV Isolates

Infectious bronchitis(IB)is a rapidly spreading respiratory disease among chickens,leading to the decline in eggs quality and growth performance of laying hens.Infectious bronchitis virus(IBV)has a variety of growing genotypes and serotypes due to the special nested copy mode of IB Vs,which caused by nested copy mode of its pathogen——Infectious bronchitis virus(IBV).This means the commercially availableized vaccines often failed to provide valid immune protection for locally prevalent IBVs.Hence,screening vaccine or vaccine candidates basing on the locally epidemic IBV strains is an important direction to prevent and control local IB base on the local epidemic IB strains to screen vaccine or vaccine candidates.In this study,five local isolates of IBV strains were tested by serum cross-neutralization test and S1 gene sequencing and analysis to screen the dominant strains by serotyping and genotyping,which will provide important references for the development of regional IB vaccines.Methods:In this study,we firstly chose tracheal organ cultures(from 18?20-day-old SPF chick embryos nic age)as culture system firstly,and determined the tracheal organ cultures-median infective dose(TOC-ID50)of five local IBV isolates(JHL strain,XPX strain,SM strain,ZDZ strain and DJ strain)were treated with tracheal organ cultures-median infective dose(TOC-ID50.Secondly,the positive sera of each strain were prepared and the serum cross-neutralization tests wereas performed on the tracheal organ cultures by fixed virus fixation-serum dilution method serum for the serotyping of IBVs.Thirdly,the S1 gene of the five IBV strains were sequenced and analyzed for the genotyping.Finally,the dominant strains were screened according to the above results and further verified by the animal regression tests.Results:(1)The TOC-ID50 of JHL,XPX,SM,ZDZ and,DJ strains were 10-6/ml,10-6.71/ml,10-5.10/ml,10-5.5/ml,10-5.72/ml,respectively.(2)The results of serum cross-neutralization test showed the correlation coefficients of antigens correlation among between JHL strain and,XPX,SM,DJ,ZDZ strain were 26%,55%,50%and 34%,respectively;the correlation coefficients of antigenscoefficient of antigen correlation between XPX strain and SM,DJ,ZDZ strains were 42%,68%and 38%,respectively;the correlation coefficients of antigenscoefficient of antigen correlation between SM strain and DJ,ZDZ strain were 45%and 47%,respectively;and correlation coefficient of antigen the coefficient of antigen correlation between between DJ and ZDZ strain wasere 52%.The correlation coefficients of antigens coefficient of antigen correlation among the five strains ranged from 26%to 68%,with the maximum between up to 68%of DJ and XPX strain,but no more than 80%.The above results showed that the five isolates were antigen-related and belonged to the different subtypes in the same serotype but different subtype.(3)The results sequencing analysis of S1 genes sequencing,analysis and genotyping showed that there were different degrees of base mutation and missing in S1 gene sequences of the five IBV strains.Based on phylogenetic analysis of Neighbor-joining S1 genes,JHL,JXL,XPX and DJ Strains strains belonged to QX-type strain;and SM isolates belonged to 4/91-type isolates;and ZDZ isolates belonged to Mass-type isolates.(4)The results of screening of dominant strains and animal regression tests results showed that:through the contrast analysis of interrelationships between serotypes and genotypes in five strains,the DJ strain was chose to carry outto immunize SPF chicks for challenge experiment;the chicks without immunization of DJ strain appeared obvious spirit depression and uratosis in kidney after challenge with other IB Vs;while no obvious clinical symptoms and lesions were found in the pre-immunized chicks.The results of hemagglutination inhibition(HI)assay showed that the HI titers of sera in 2-week-age pre-immunized chicks(1th week after challenge)were between 3.4log2 and 3.9log2,and the HI titers increased gradually at 2?5-week age,and the HI titers of sera in 5-week-age chicks were between 5.7log2 and 6.5log2.As for the unpre-immunized chicks,the HI titers of sera in 4-week-age chicks were between 3.6log2 and 4.4log2,and then there was a increasing trend in HI titers.The serum antibodies with higher HI titers in the immunized chicks were produced earlier than those in the non-immunized chicks.animal experiments;through hemagglutination inhibition test,the strain in immune control group grew at 7log2 with in 3 weeks,reached 7.21og2 at the highest level and had a tendency to maintain antibody titers.The above results showed that pre-immunization with DJ strain could provideplay a better protection against challenge with other four IBV isolates.protective effect on the other four isolates.Conclusions:JHL,XPX,SM,ZDZ and DJ isolates were are all different subtypes of the same serotype;The genotypes of JHL,XPX and DJ isolates were are QX type;and SM isolate is similar to the 4/91 type;and ZDZ isolate is was Mass type;the DJ strain iswas the dominant strain screened in this experiment.