2011-2012Isolation And Identification Of IBDV And Antigenicity Study Of IBDV Strains Of Different Genotypes

Infectious bursal disease (IBD) is a highly infectious,immunosuppressive disease of young chickens of three-to-twelve-weeksold. Infectious bursal disease virus (IBDV) is the etiological agent of thedisease.The immunosuppression caused by IBDV could result in the highsusceptibility to other disease and lower level of immune response tovaccines, such as New Castle Disease and avian influenza in the flocks.Partially protection or immune failure in the vaccinated flocks dued to theemergence of new subtypes.Therefore, it is important and essential toisolate the epidemic isolates and screening for the candidate strain orstrains by testing of immunogenicity and cross immunity protection.Firstly,20infectious bursal disease virus were isolated from the IBDsuspected chicken flock by chicken embryo inoculation of theFabricus′bursa suspension via chorio-allantoic membrane (CAM) fromGuangxi, and Jiangsu the two provinces in2011-2012years.Thesequences analysis of VP2hypervariable region (vVP2) from IBDVgenome segment A indicated that, the19isolates,such as YY1195，QX110606and so on,were classified to be potent virulent IBDV(vvIBDV) according to critical amino acid sequences about222-A、249-Q、254-G、256-I、279-D、284-A、294-I and299-S,and showed95.7%~100%homology to vvIBDV. Furthermore, in the phylogeneticanalysis, the19isolates were grouped with vvIBDV reference strains.Onthe other hand,separation strains QX110603has222-P,279-N,284-T,299-N cIBDV features amino acid sites, homology with the attenuatedvaccine strain was higher (98.1%~98.7%), in the phylogenetic analysis,the QX110603was grouped with cIBDV reference strains.Inaddition, most of these isolates showed unique amino acid mutation inD212N, which is a mutation occurred in the first water area may causechanges in strains of hydrophilic and thus affecting the antigenicity of thevirus, howere, these strains were isolated from vaccinated chickens soinfer some antigenic drift strain may have occurred.Serum neutralizationtest shows that20isolates with TSC-1and HUN0801, B87(3) asbelonging to a serum isoforms.Secondly, four isolates were used to infection non-vaccined-4-weekchickens to compare and determine their pathogenicity by analyzing thelethality，immune organs index,(IOI),immune cell content respectively,and target organs in the viral load.The results showed that there wassignificant diffrences of4evaluation indicators between the infectedgroups and the un-infected groups (p<0.05),even all the four isolatescould induced morbitities of100%, indiecated that there is differenceamong the isolates on pathogenicity with the highest lethality(30%),which is isolate of NN1172. Further more,NN1172strain infectedbursa and thymus tissue in the maximum number of IBDV copies,respectively (13.63±0.44)*103number copies/μl and (14.07±0.38)*103number copies/μ l, bursal lymphocytes in thymus tissueconcentration differences between the control group and the mostremarkable, show that NN1172on the strongest local commercial chickenpathogenic.Thirdly, through the preparation of four isolates of monovalentinactivated oil-emulsion vaccine (OEV) as well as merchandise B87(in)vaccine strain the OEV and respectively immune cross protectionexperiments on4isolates.Experimental challenge after each strainseparately OEV immune chicken IOI group, immune protectionindex,(IPI), immune cell contents and evaluation of the viral load in theorganization.Results show, the protection of B87(in) OEV againstNN1172, NN1005, GD10111, JS7, were70%,60%, and80%,respectively, indicating commodities vaccine B87(in) could not providefully protection against field strains;Protections of100%were observedon the birds vaccinated with OEV of the4isolates against the homogeneous viruses, and the protcetions of OEV of NN1172againstisolates NN1005，GD10111and JS7were the best by80%，80%and90%respcetively, while those of the other three isolates were divergent(50%-80%);in addition, OEV of the NN1172,there was least significantdifference on IOI, IPI, immune cell contents and evaluation of the viralload between the infected groups and the un-infected groups than theother OEV. It is concluded that the immune efficacy of multivalent OEVwas the best among all the OEVs tested，which may be a good vaccine forPrevention and control of IBD in Guangxi.