Kawaoka Y, Nestorowicz A, Alexander D J, Webster R G
Virology. 1987 May;158(1):218-27. doi: 10.1016/0042-6822(87)90256-x.
Comparative sequence analysis of the hemagglutinin (HA) genes of a highly virulent H5N8 virus isolated from turkeys in Ireland in 1983 and a virus of the same subtype detected simultaneously in healthy ducks showed only four amino acid differences between these strains. Partial sequencing of six of the other genes and antigenic similarity of the neuraminidases established the overall genetic similarity of these two viruses. Comparison of the complete sequence of two H5 gene sequences and partial sequences of other virulent and avirulent H5 viruses provides evidence for at least two different lineages of H5 influenza virus in the world, one in Europe and the other in North America, with virulent and avirulent members in each group. In vivo studies in domestic ducks showed that all of the H5 viruses that are virulent in chickens and turkeys replicate in the internal organs of ducks but did not produce any disease signs. Additionally, both viruses isolated from turkeys and ducks in Ireland were detected in the blood. These studies provide the first conclusive evidence for the possibility that fully virulent influenza viruses in domestic poultry can arise directly from viruses in wild aquatic birds. Studies on the cleavability of the HA of virulent and avirulent H5 viruses showed that the principles established for H7 viruses (F. X. Bosch, M. Orlich, H. D. Klenk, and R. Rott, 1979, Virology 95, 197-207; F. X. Bosch, W. Garten, H. D. Klenk, and R. Rott, 1981, Virology 113, 725-735) also apply to the H5 subtype. These are (1) only the HAs of virulent influenza viruses were cleaved in tissue culture in the absence of trypsin and (2) virulent H5 influenza viruses contain a series of basic amino acids at the cleavage site of the HA, whereas avirulent strains contain only a single arginine with the exception of the avirulent Chicken/Pennsylvania virus. Thus, a series of basic amino acids at the cleavage site probably forms a recognition site for the enzyme(s) responsible for cleavage.
对1983年从爱尔兰火鸡中分离出的高致病性H5N8病毒的血凝素（HA）基因与同时在健康鸭中检测到的同一亚型病毒进行的比较序列分析表明，这些毒株之间仅存在四个氨基酸差异。对其他六个基因的部分测序以及神经氨酸酶的抗原相似性确定了这两种病毒的总体遗传相似性。对两个H5基因序列的完整序列以及其他强毒株和无毒株H5病毒的部分序列进行比较，为世界上至少两种不同的H5流感病毒谱系提供了证据，一种在欧洲，另一种在北美，每组中都有强毒株和无毒株成员。在家鸭体内进行的研究表明，所有对鸡和火鸡具有致病性的H5病毒都能在家鸭的内脏中复制，但不会产生任何疾病迹象。此外，在爱尔兰从火鸡和鸭中分离出的两种病毒都在血液中被检测到。这些研究首次提供了确凿证据，证明家禽中完全致病性的流感病毒可能直接源自野生水鸟中的病毒。对强毒株和无毒株H5病毒HA裂解性的研究表明，为H7病毒确立的原则（F. X. Bosch、M. Orlich、H. D. Klenk和R. Rott，1979年，《病毒学》95卷，197 - 207页；F. X. Bosch、W. Garten、H. D. Klenk和R. Rott，1981年，《病毒学》113卷，725 - 735页）也适用于H5亚型。这些原则是：（1）只有强致病性流感病毒的HA在没有胰蛋白酶的组织培养中被裂解；（2）强致病性H5流感病毒在HA裂解位点含有一系列碱性氨基酸，而无毒株除了无毒的鸡/宾夕法尼亚病毒外仅含有单个精氨酸。因此，裂解位点的一系列碱性氨基酸可能形成了负责裂解的酶的识别位点。
