| Newcastle disease (ND) is a highly contagious and fatal disease which could cause substantial economic losses in poultry industries. ND has experienced four major panzootics in worldwide since its emergence in 1926. Its aetiology is Newcastle disease virus (NDV) which belongs to the newly defined genus Avulavirus as a member of the family Paramyxoviridae. In this study, 20 NDVs were isolated from some poultry farms in Jiangsu province and phylogenetic analysis was then conducted based on the fusion (F) and hemagglutinin-neuraminidase (HN) glycoprotein gene sequences, respectively. In addition, to explore the molecular mechanisms for the significant different pathogenicity between chicken and pigeon-origin NDVs, complete genome sequences of four pigeon-origin NDVs were also sequenced and analyzed in this paper.1. Characterization of NDVs isolated during 2007-2008Twenty NDV strains were isolated from outbreaks in chicken, pigeon and goose flocks in Jiangsu province during 2007 and 2008. The F gene sequence for each isolate was then amplified and sequenced. Phylogenetic tree, based on F genes of the 20 isolates as well as some representative sequences in GenBank, showed that all these newly strains belonged to 5 genotypes: two strains were in genotyope ? , six were in genotyopeâ…¡, four pigeon-origin strains were in genotypeâ…¥b, seven were in genotypeâ…¦d and one was in Class ?. Homology comparison showed that the genotype ? andâ…¡NDVs were either V4 or LaSota-like strains, which demonstrated that the vaccine strains were used widely in the poultry flocks in China. The strain ascribed in Class? showed low genetic similarity with DER49/99, one ClassI strain from America. The results mentioned above showed that a variety of NDV genotypes were co-existent in Jiangsu province and the genotypeâ…¦d virus was still prevalent in poultry farms.Alignment of the HN protein sequences from these 20 isolates revealed that there were 585 or 616 amino acids (aa) in length for genotype ? strains, 577aa for genotypeâ…¡strains and 571aa for genotypeâ…¥andâ…¦strains. The phylogenetic tree based on the HN genes was similar to that on the F genes, indicating the integrated evolution in NDV genome.For genotype VII NDVs, the pathogenicity determined by mean death time (MDT), intracerebral pathogenicity index (ICPI) and intravenous pathogenicity index (IVPI) was consistent with that determined by F protein cleavage site sequences, while the pathogenicity of genotype VI NDVs was not. Besides, based on the reactivity of the isolates with a panel of monoclonal antibodies (Mab) against the F or HN glycoprotein, significant antigenic difference could be observed among these NDV isolates.2. Determination and analysis of the genome sequences of four pigeon-origin NDVsThe whole genome sequences of the four pigeon-origin Newcastle disease viruses were obtained by RT-PCR, cloning and sequencing. The genomes of the four strains were all 15,192nt in length, and the additional six nts were located in the same position as the NDV strains in genotypeâ…¦. Phylogenetic tree based on the variable region of F genes revealed that the four pigeon-origin strains were ascribed to sublineage EU/re (recent European, EU/re) in the subgroup ofâ…¥b, the same as the predominant pigeon-origin strains isolated from Europe and Japan during 1987-2002, indicating the closing relationship in NDV epidemiology among these regions. Phylogenetic tree based on the whole genome was identical with that on the F or HN genes, indicating that individual genes were evolved in the context of entire NDV genome. Homology comparison of each protein between the genotypeâ…¥strains and other genotypes showed that the L gene is the most conserved gene while the P gene was the most variable one, and that the genotypeâ…£,â…¦andâ…§strains shared high identities with genotypeâ…¥strains indicating the closing phylogenic relationship of these genotype strains. Comparison of major substitutions in genotypeâ…¥NDV genomes with those in the other genotype NDVs revealed that several characteristic amino acid residues of pigeon-origin NDVs were present in nucleocapsid protein (N463D, P469I, P477H), phosphoprotein (D10E, T93K/R, R163G), large protein (N1110T/A, A1757V) and HN protein (G122R), respectively. However, no typical substitution was found in matrix (M) and F proteins. On the basis of the fact that phenotype is determined by gene sequence, we postulated that these changes might alter the conformation of the related proteins, thus affecting the virulence and host-specificity of these pigeon-origin strains. To verify this postulation, additional work is under the way in our lab now.
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