The Investigation On The Molecular Epizootiology Of Chicken Newcastle Disease Virus Isolated From Hebei Province

Twelve isolates of virus which could agglutinate chicken red blood cell were isolated from sick or dead chickens in different parts of Hebei province. These agglutinations were inhibited and neutralized by Newcastle disease virus standard antiserum. These isolates were confirmed to be Newcastle disease virus based on HA and HI test and were named by HBB, HBBa, HBC, HBCh, HBH, HBHa, HBL, HBQ, HBS, HBT, HBX and HBZ. The isolates were identified and studied on their biological characteristics. The results showed that the twelve NDV isolates are hemagglutination (HA) active and hemagglutination inhibition (HI) active, and the pathogenicity to chicken embryo could be inhibited by ND positive serum. Pathogenicity of the isolates was identified. By means of the test of mean death time (MDT) of chicken embryo, intracerebral pathogenicity index (ICPI) of 1-day-old chicken and intravenous pathogenicity index (IVPI) in 6-week-old chicken, HBC and HBQ strains were verified to be lentogenic strains, and the other strains were all virulent.The Main function fragment of Fusion gene of 12 NDV isolates were amplified by revers transcription-polymerase chain reaction (RT-PCR) and sequenced after being cloned into PBS-T plasmids. Gene F of 389bp (1bp～389bp) and their corresponding amino acid sequence (1～130 amino acid residues) of the NDV strains, including the 12 isolates and 22 typical strains from Genebank, were compared and analyzed. The phylogenetic tree system was constructed based on the obtained nucleotide (from 1 to 389bp), and the virulence and genotype of 12 isolates were confirmed. The results showed that none of the F genes of the isolates suffered any base deletion and insertion, but there are mutations in many points scattering about. The homologous rate of F gene nucleotides sequences was 81.2%～99.7%, and of the deduced amino acid sequences was 77.5%～100%. The F gene sequences from 12 isolates shared a high identity between 80.5%～98.5% with that of related sequences reported home and abroad. The amino acid residues predicted, shared an identity between 77.5%～97.7% with that of other strains. The results showed that the 12 isolates can be divided obviously into three groups. The nucleotide sequence and deduced amino acid sequences of this fragment of 12 NDV isolates were compared with that of published NDV F genes respectively. Their homology was higher in the same group and lower between the groups. There were 7 strains in the first group, 3 strains in the second group and 2 strains in the third group. The NDV isolates in group 1, 2, 3 belonged to genotypeⅦ,ⅥandⅡrespectively.The results revealed that the NDV epidemic in Hebei province was complicated and all the isolates belonged to 3 genotypes (Ⅱ,ⅥandⅦ). Most of the isolates were classified into genotypeⅦ. It indicated that the genotypeⅦNDV was the major pathogeny causing the epizootic of ND in Hebei province.