title: Characterization of emerging Newcastle disease virus isolates in China.
abstract: BACKGROUND
  Newcastle disease (ND) is a devastating worldwide disease of poultry characterized by increased respiration, circulatory disturbances, hemorrhagic enteritis, and nervous signs. Sequence analysis shows several amino acid residue substitutions at neutralizing epitopes on the F and HN proteins of recent Shaanxi strains. Both Cross protection and cross serum neutralization tests revealed that the traditional vaccine strains were unable to provide full protection for the flocks.
  
  
  METHODS
  To better understand the epidemiology of Newcastle disease outbreak, a portion of the F gene and the full-length HN gene were amplified from Shaanxi isolates by reverse transcription-polymerase chain reaction (RT-PCR) and then conducted sequence and phylogenetic analyzes. In pathogenicity analysis, both high intra-cerebral pathogenicity index (ICPI) and mean death time (MDT) tests of chicken embryo were carried out. Furthermore, a cross-protection experiment in which specific-pathogen-free chickens vaccinated with a LaSota vaccine strain were challenged by the recent Shaanxi strain was also performed.
  
  
  RESULTS
  Nine Newcastle disease (ND) virus (NDV) isolates which were recovered from ND outbreaks in chicken flocks in China were genotypically and pathotypically characterized. Amino acid sequence analysis revealed that all the recent Shaanxi-isolated NDVs have (112)R-R-Q-K-R-F(117) for the C-terminus of the F2 protein and exhibit high ICPI and MDT of chicken embryos, suggesting that they were all classified as velogenic type of NDVs. Phylogenetic analysis of these isolates showed that they belong to subgenotype VIId that have been implicated in the recent outbreaks in northwestern China. The percentage of amino acid sequence identity of F protein between recent Shaanxi stains and five vaccine strains was in the range of 81.9 %-88.1 %, while the percentage of amino acid sequence identity of HN protein between recent Shaanxi strains and vaccine strains was in the range of 87.4 %-91.2 %. Furthermore, a number of amino acid residue substitutions at neutralizing epitopes on the F and HN proteins of these isolates were observed, which may lead to the change of antibody recognition and neutralization capacity. A cross-protection experiment indicated that specific-pathogen-free chickens vaccinated with a LaSota vaccine strain was not capable of providing full protection for the flocks that were challenged by the recent Shaanxi strain.
  
  
  CONCLUSIONS
  Taken together, our findings reveal that recent Shannxi NDVstrains exhibit antigenic variations that could be responsible for recent outbreaks of NDVs in northwestern China.
authors.affiliation: College of Veterinary Medicine, Northwest A & F University, Yangling, 712100, China. wjingyu2004@126.com.
authors.forename: Jing-Yu
authors.initials: JY
authors.lastname: Wang
authors.affiliation: College of Veterinary Medicine, Northwest A & F University, Yangling, 712100, China. 550676754@qq.com.
authors.forename: Wan-Hua
authors.initials: WH
authors.lastname: Liu
authors.affiliation: College of Veterinary Medicine, Northwest A & F University, Yangling, 712100, China. 1015382207@qq.com.
authors.forename: Juan-Juan
authors.initials: JJ
authors.lastname: Ren
authors.affiliation: College of Veterinary Medicine, Northwest A & F University, Yangling, 712100, China. 419331091@qq.com.
authors.forename: Pan
authors.initials: P
authors.lastname: Tang
authors.affiliation: College of Veterinary Medicine, Northwest A & F University, Yangling, 712100, China. 252303040@qq.com.
authors.forename: Ning
authors.initials: N
authors.lastname: Wu
authors.affiliation: Department of Veterinary Medicine, National Pingtung University of Science and Technology, Pingtung, 912, Taiwan. wuhy@mail.npust.edu.tw.
authors.forename: Hung-Yi
authors.initials: HY
authors.lastname: Wu
authors.affiliation: Department of Veterinary Medicine, National Pingtung University of Science and Technology, Pingtung, 912, Taiwan. cdchang@mail.npust.edu.tw.
authors.forename: Ching-Dong
authors.initials: CD
authors.lastname: Ching
authors.affiliation: Institute of Molecular Biology, National Chung Hsing University, Taichung, 402, Taiwan. hjliu5257@nchu.edu.tw.|Agricultural Biotechnology Center, National Chung Hsing University, Taichung, 402, Taiwan. hjliu5257@nchu.edu.tw.|Rong Hsing Research Center for Translational Medicine, National Chung Hsing University, Taichung, 402, Taiwan. hjliu5257@nchu.edu.tw.
authors.forename: Hung-Jen
authors.initials: HJ
authors.lastname: Liu
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002645:Chickens; D002681:China / Q000453:epidemiology; D021821:Communicable Diseases, Emerging; D003429:Cross Reactions; D000939:Epitopes / Q000276:immunology; D015707:HN Protein / Q000235:genetics / Q000276:immunology; D006385:Hemagglutination Inhibition Tests; D008969:Molecular Sequence Data; D009500:Neutralization Tests; D009521:Newcastle Disease / Q000453:epidemiology* / Q000821:virology*; D009522:Newcastle disease virus / Q000145:classification* / Q000235:genetics* / Q000302:isolation & purification; D010802:Phylogeny; D017422:Sequence Analysis, DNA; D014760:Viral Fusion Proteins / Q000737:chemistry / Q000235:genetics; D014765:Viral Vaccines / Q000276:immunology; D017201:Virus Shedding
chemical_list: D000939:Epitopes; D015707:HN Protein; D014760:Viral Fusion Proteins; D014765:Viral Vaccines