Isolation and identification of high virulent strains of NDV and immune protection of newcastle disease virus

Two isolates having haemagglution property have been isolated from the disease-infected chicken house in Baoding of Hebei Province,the haemagglution property of the two isolates can be inhibited by the positive antiserum of NDV,not by the positive serum of AIV(H9 subtype),and EDS76,which shows that the two strains are NDV.The result of pathogenicity tests(MDT,ICPI,IVPI) show that the two NDV isolates claim these data: MDT,40.8 h and 53.7 h;ICPI,1.96 and 1.86;IVPI,2.89 and 2.72,which indicates that the two NDV isolates are highly virulent.Inactivated oil-emulsion vaccine was made by isolated strain of HBW.The efficacy were compared between inactivated LaSota vaccine and isolates inactivated vaccine and the experiment of cross-protection of vaccine assess by immunized chickens with isolate inactivated and LaSota inactivated vaccine.Result showed that(1) There is no apparent difference of HI antibody between chickens inoculated with isolates inactivated vaccine and inactivated LaSota vaccine during all experiment period;(2) All chickens with higher than 6log2 HI titer inoculated with isolates inactivated vaccine could obtain 100% protection against F48E9 and two isolated strains,while all chickens with higher than 6log2 HI titer inoculated with LaSota inactivated vaccine could not obtain 100% protection against F48E9 and two isolated strains.Result showed that variation of pathogenicity and antigenicity exist among the strains of NDV of different genotypes.