[Molecular characterization of a genotype II virulent Newcastle disease virus isolate from chicken]

Newcastle disease virus (NDV) field strain SQZ04 was isolated from a broiler flock with typical symptoms and lesions, and cloned by plaque-purification three times. NDV SQZ04 was determined as a virulent strain with MDT of 50.5h and 51.2h, ICPI of 2.0 and 1.92, IVPI of 2.8 and 2.68 respectively before and after plaque-purification. Analysis of F gene indicated that SQZO4 was determined as a virulent gene type II , and its protein amino acid sequence has homologies of 99.3% , 98.7% and 96.9% with published gene type II vaccine strains LaSota, B1, virulent strain Taxas48,much higher than homologies of 88.3% - 88.6% or 91.3% - 92.1% with published gene types VI and IX. This is the first virulent field strain of gene type UI reported in China. Further more, the amino acid sequence 111 GGRQGRL117 in the F protein cleavage site in SQZ04 strain is identical to lentogenic strains of NDV, such as vaccine strains LaSota, B1. This is the first report that virulent NDV could have lentogenic amino acid sequence in the cleavage site of F protein, where HN genes was compared SQZ04 has a higher homologies of 95.3%- 97.3% with known velogenic strains, but lower homologies of 87.8% - 89.5% with published lentogenic strains.