Genetic characterization and phylogenetic analysis of Newcastle disease virus from China

The avian infectious disease, Newcastle disease (ND), caused by Newcastle disease virus (NDV) can cause severe economic losses to poultry whether vaccinated or not in many countries. In this study, a strain of NDV isolated from an outbreak in China was subjected to biological, phylogenetic and genetic characterization. The results showed that the mean death time (MDT) was 52.4 h and the intracerebral pathogenicity indices (ICPI) value was 1.95. In addition, amino acid sequencing result showed that it had a sequence ¹¹²R-R-Q-R-R^↓F¹¹⁷ at fusion protein cleaving site (FPCS) indicating a velogenic strain. And its genome length is 15,192 nucleotide (nt) with the conserved complementary 3' leader and 5' trailer regions encoding six genes, 3'-NP-P-M-F-HN-L-5'. Based on phylogenetic analyses for hyper-variable region and complete genome of F gene, the strain studied here can be clustered into genotype IX, Class II, which has little evolution distance with strains of genotype III, being considered as a transitional strain in the evolution history of NDV. The rescue of infectious cDNA is proceeded in 9-day-old embryonated SPF chicken eggs. Despite the death of the first generation, the allantoic fluid harvested from the first generation lost its pathogenicity after passage. And we found the phenomenon happened due to the antibody appearing in the allantoic fluid. These findings offer our understanding of circulating strains of NDV in China and lay scientific foundations for making more efficient vaccines for Newcastle disease.