| Newcastle disease(ND), Asian Fowl pest, is one of the most highly pathogenic viral diseases of avian species because it causes high mortality and morbidity rates. ND is caused by NDV, which is also known as avian paramyxovirus type 1(APMV-1); this virus belongs to the genus Avulavirus and subfamily Paramyxovirnae(family Paramyxivirinae, order Mononegavirales). The NDV genome is non-segmented and contains single-stranded negative-sense RNA, with six transcriptional units in the order 3′-NP-P-M-F-HN-L-5′and followed the ’rule of six’and encode six structural proteins and two additional non-structural proteins. NDV is generally categorised based on pathogenicity in chickens into three pathotypes, namely, velogenic, mesogenic or lentogenic.NDV has a wide host range and it has been demonstrated in at least 250 species in most orders of birds. The Africa ostrich is the biggest bird on the earth and also is an kind of susceptible host for NDV. Newcastle disease(NDV) is an important pathogen disease to ostrich and it can cause mortality and morbidity in ostrich flocks. However, the young and adult ostriches often show marked different clinical symptoms when infected with NDVs.The mainly results of the research study as follows:1. In October 2006, tissue samples,including liver,lung,heart,spleen, and kidney of some infected ostrich birds were collected from some breeding bases of Shaan xi Province,northwest of China. A ostrich-origin NDV isolate, which was abbreviated as NDV/Ostrich/SX-01/06,obtained by HA, HI, and RT-PCR.2. The sequence of complete genomic and assessment results of pathogenicity of the isolate. Ten overlapping fragments covering the full-length genome of this NDV isolate was amplified by RT-PCR. The genome was assembled with the software suit DNASTAR. The NDV isolate genome, with 15,198 nt in length, comprised six ORFs in the order3′-NP-P-M-F-HN-L-5′. The pathogenicity index of this strain was evaluated, which exhibited an mean death time(MDT) of 86 h and intracerebral pathogenicity index(ICPI) of 0.113.However, NDV/Ostrich/SX-01/06 exhibited discordance between its lentogenic ICPI and its virulent fusion protein cleavage site motif 112R-R-Q-K-R-F117, which is typical molecular characteristic of a virulent NDV strain. The study firstly fully sequence and analyses the genome of this strain, and show that there are several virulence gene which involved in theprocesses of viral virulence regulation.3. The results of deduced amino acids and nucleotide acids of F and HN of NDV/ostrich/SX-01/06 shown that 11 and 3 amino acid substitutions were identified in the functional domains of F and HN proteins, respectively, which were compared with mostly other Class II NDV isolates. There was no amino acid subsititution in neuralising epitopes of F. However,analysis of the amino acids of neutralising epitopes of HN proteins showed 5amino acid substitutions,in the isolate,which were compared with other Class II NDV strains.The results shown that the continuous evolutionary divergence in NDVs due to various immunity pressure.4. The analysis of evolutionary tree of this Ostrich-origin NDV. A phylogenetic tree was constructed based on the complete sequences of the F gene by using MEGA 6.02. This NDV isolate was classified into genotype VIi in Class II. NDV/ostrich/SX-01/06 in this study showed 99.9% nucleotide homology with Shaanxi 10(Accession number: KC853020), a velogenic genotype VIi NDV strain isolated from crested ibis(Nipponia Nippon) in 2010.The nucleotide sequence homologies of this isolate was 31.8% with the LaSota strain, which was vaccine strain widely used in China. This fistly report ostrich-origin NDV, which was clustered into new genotype VIi. This study show that genotype VI NDVs have a wide susceptible host, and wild bird play an important role in the transmission and distribution of this genotype NDV. |
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