Study On Genetic Variation Of Some Fusion Protein In High Virulent Strains Of Newcastle Disease Virus And Its Antigenicity

The genes in the protein F cleavage site region of 4 strains of Newcastle disease virus (NDV) were cloned and their gene sequences were measured after amplified by RT-PCR. Two strong virulent strains are isolated from the NDV-infected poultry farms in Baoding of Hebei Province, and were respectively named HBB and HBW. Two strains of the others were the standard strong virulent strain F₄₈E₉ and the vaccinal strain LaSota. Then their homogeneity was compared with those of different genotype typical strains and their violence was analyzed. Gene F of 389 bp (1-389 bp) and their corresponding amino acid sequence(1-130 amino acid residues) of 37 NDV strains, including the 4 strains and 33 typical strains from Genbank, were compared and analyzed. The phylogenetic tree system was established, and the genotypes of the 2 isolated strains have been decided. The result showed that there is a low homogeneity between F₄₈E₉ and LaSota or the two isolated strong virulent strains, with homogeneity ranging from 83.8% to 84.1% in nucleotide and 84.4%⁸6.6% in amino acid residue. However, between two isolated strong virulent strains, there was a low homogeneity of 88.2% in nucleotide, and there was a high homogeneity of 93.9% in amino acid residue. The cleavage site of F protein of F₄₈E₉ is ¹¹²RRQRRF¹¹⁷, while the two strains isolates have the cleavage site-¹¹²RRQKRF117, which is in agreement with the characteristics of high virulent strains and the results of pathogenic tests. None of the F genes of the isolated NDV virulent strains suffered any base deletion and insertion, but there are mutations in many points scattering about. The amino acids of 55 to 61, 72, 84 to 89 and 128 to 130 in the isolated strains are all highly conservative, and their mutation points were mainly located between 101 and 111. The genotype of HBB in the isolated NDV strains belongs to the typical genotypeâ…¥, and that of the HBW belongs to the genotype â…¦.At the same time, inactivated oil-emulsion vaccine was made by isolated strain of genotype â…¦ of NDV. After the vaccination with the inactivated LaSota strain vaccine and inactivated isolated strain vaccine, their immuning effects were compared, and cross-protection test. The result showed that there is apparent difference in the antibody titer of HI between the samples from vaccination group and the control group. There is no apparent difference in the antibody titer of HI between chickens inoculated with isolates inactivated vaccine and inactivated LaSota vaccine during all experiment period. There is also a same varing tendency between the two groups. At the days of 21, 28 and 35 after inoculation (the HI titer were higher than 61og2) with isolated inactivated vaccine couldobtain 100% protection against the attacks both with F4gE9 and the isolated strains. LaSota inactivated vaccine (the HI titer were higher than 61og2) could provide 100% protection against the attack with F48E9 in these periods and the attacks with genotype VI of HBB strain. The protection rate against other isolated strains was 80%, having not reach 100%. It indicated there are differences in the antigenicity among the strains in different genotypes of NDV.Comprehensive analyses of the cross-protection and genetic variation showed that that the antigenic difference variation does exist among the vaccinate strain of LaSota and the currently epidemic strains of NDV.