Isolation,Identification of Four Newcastle Disease Virus Strains and Study on Their Biological Characteristics and Genetic Characteristics

In order to study the relationship and evolution between the latest Newcastle disease virus (NDV) epidemic strain and the vaccine strain (Mukteswar,La Sota and Clone 30 strains),four NDV epidemic strains were initially isolated and identified from immunized chicken groups in Guangdong,Guangxi and Hainan provinces. Fusion (F) gene and hemaglutinin neuraminidase (HN) gene of four isolated stains were amplified,cloned and sequenced by RT-PCR method,and the homology analysis of amino acid sequences deduced by F and HN genes of NDV and other strains published in GenBank were studied, the phylogenetic tree were build,and the pathogenicity index of each strain (EID₅₀,MDT, ICPI and IVPI) were determined. The results showed that the EID₅₀,MDT,ICPI and IVPI of the HN-08 strain were 10^-8.37/0.2 mL,58.5 h,1.78 and 2.45,that of the XX-08 strain were 10^-6.50/0.2 mL,75.0 h,1.61 and 2.41,that of the YS-09 strain were 10^-7.75/0.2 mL,64.5 h,1.71 and 2.38,and of the LF-09 strain were 10^-7.60/0.2 mL,63.8 h,1.84 and 2.38.In this experiment,the similarity of amino acid sequences of F and HN genes was over 95.8% among four strains of NDV isolated from chicken,the similarity of four NDV strains with chicken epidemic strains (GX11/03 and GM strains),vaccine strains (Mukteswar,La Sota and Clone 30 strains) and standard virulent strain (F₄₈E₉ strain) were from 96.8% to 98.6%,86.7% to 90.6% and 88.4% to 91.3%,respectively. The results showed that four NDV epidemic strains were virulent strains,which were closely related to the GX11/03 and GM strains that were popular in China in recent years,but relatively far from the traditional vaccine strains.