Newcastle disease outbreaks in western China were caused by the genotypes VIIa and VIII

Abstract

Twelve Newcastle disease virus (NDV) strains were isolated from chickens involved in outbreaks of Newcastle disease (ND) in western China (Shaanxi, Gansu, Xinjiang, Qinghai and Guangxi provinces) between 1979 and 1999. All strains were determined to be velogenic by plaque formation, the mean death time (MDT) of embryonated eggs, and the intracerebral pathogenicity index (ICPI). For preparation of virus RNA, the acid guanidinium-thiocyanate method was used. A 908bp fragment of nucleotide was amplified by RT-PCR starting from the N terminal of the F gene and the PCR segments were cloned into the PGEM-T vector and sequenced. The similarities of the nucleotide sequences (1-519bp) and predicted amino acid sequences of the F gene (1-125) were analyzed by comparing the 12 NDV isolates with the NDV vaccine strains Lasota, B1, H1 and V4, with classical NDV strains and recent epizootic strains. Phylogenetic analysis demonstrated that all strains were of two novel genotypes; the NDV strains that caused the outbreak of ND in western China during 1998-1999 was of the genotype VIIa, whereas the strains from the Qinghai province (1979-1985) were of genotype VIII, which has been found predominately in southern Africa.