中文摘要：

从西藏病死藏鸡中分离到具有血凝活性的病毒、经血凝抑制试验、电镜观察、PCR扩增和测序鉴定为新城疫病病毒（NDV），通过动物致病性试验证明该病毒对鸡具有致病性；分离毒株毒力测定结果显示，MDT为120h，EID50为10^-8.44、IVPI为0．5、ICPI为0．6，均符合NDV弱毒株特征。血凝解脱及血凝素热稳定性试验显示：各分离株的血凝解脱时间短，血凝素热稳定性较差，符合NDV弱毒株的特征。F基因的序列测定遗传进化分析表明，西藏分离毒株之间的核苷酸序列具有99％的同源性，与疫苗株LaSota的同源性为90％；与国内标准强毒株F48E8同源性为81％。推导其氨基酸序列分析表明，各分离株的F蛋白的裂解位点氨基酸^112G-K-Q-G-R-L^117，具有NDV弱毒株特征，与毒力测定结果相符。本研究首次报道了NDV西藏分离毒株遗传进化情况和生物学特性情况，为进一步研究高海拔、缺氧环境下NDV生物学特性变化研究奠定了基础。

英文摘要：

Newcastle disease virus （NDV） virus with hemagglutination activity were isolated from the dead chickens in Tibet and were identified by the hemagglutination inhibition test, RT-PCR and sequencing, furthermore it proved that the viruses were pathogenic to chickens by pathogenicity test,in which MDT, EID50, IVPI and ICPI were 120 h, 10^-8.44/mL,0.5 and 0.6 indicating that it the characteristic of attenuated strain of Newcastle disease virus. The he- magglutinating free and hemagglutining thermal stability test showed that hemagglutinating free time was short,and the thermal stability of hemagglutinin was low,being in line with the characteristics of avirulent NDV. The phyloge netic analysis of F genes showed nucleotides sequence homology was 99% among the Tibet strains, the homology with the vaccine strain LaSota and standard virulent strain F48E8 was 90% and 81% respectively. Deduced amino acid sequence analysis showed that the cleavage site amino acids of F protein were ^112 G-K-Q-G-R-L^117, similar to the characteristics of attenuated NDV, which were consistent with the pathogenicity test. This paper first reported the genetic evolution and biological characteristics of NDV strains isolated in Tibet which is contributed to further study the biological characteristic changes of NDVviruses in high altitude,hypoxie environment.