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H7N9病毒正在适应人类
来源:大地网——行中国看天下  作者:秦铭 【 】  2013-04-22

    美国媒体称,对导致多名中国人死亡的禽流感病毒所做的基因分析描绘出一种不断进化以适应人类细胞的病毒,这引发了人们对它可能会引发新的全球性流感疫情的担忧。
    美国每日科学网站4月12日指出,这项合作研究是由以日本国立感染症研究所流感病毒研究中心的田代真人、威斯康星大学麦迪逊分校和东京大学的河冈义裕领导的小组完成的,该研究刊登在《欧洲监控》周刊的最新一期上。这一小组研究了从该病原体的四名受害人身上分离出的H7N9病毒以及从禽类和上海一市场附近的环境中分离出的样本的基因序列。
  禽流感领域的着名专家河冈义裕说:“从人身上,而不是从禽类和环境中分离出来的病毒发生的蛋白质变异让病毒能够在人类细胞中高效生长,也让它们能在与人类上唿吸道吻合的温度下生长,这一温度低于我们在禽类身上发现的温度。”
  报道称,这些从中国研究者存入某国际数据库的基因序列中获得的发现提供了有关一种令人不安的新型禽流感的首批分子层面的线索,中国疾病预防控制中心3月31日上报了首例人感染这种禽流感的病例。河冈义裕说,尽管预测它可能会引发大疫为时过早,但有明确迹象显示这种病毒正在适应哺乳动物,尤其是人类宿主。
  报道指出,流感病毒要高效地复制和传播靠的是附着和强占其宿主的活细胞的能力。尽管禽流感鲜少感染人类,但有时可以适应人类,对人类健康构成严重威胁。河冈义裕和他的同事在《欧洲监控》的报告中断言:“这些病毒拥有哺乳动物流感病毒的若干典型特征,这些特征多半有助于它们获得感染人类的能力,且会引起人们对它们可能会引发大疫情的担忧。”
  据悉,河冈义裕是威斯康星大学麦迪逊分校兽医学院的教员,同时在东京大学任职,他解释说,研究中大部分病毒——不管是来自人类还是禽类——表面的蛋白质血凝素都表现出变异现象。河冈义裕说,这些变异让它们能轻易感染人类细胞。

Could New Flu Spark Global Flu Pandemic?
New Bird Flu Strain Seen Adapting to Mammals, Humans
ScienceDaily, Apr. 12, 2013
Apr. 12, 2013 — A genetic analysis of the avian flu virus responsible for at least nine human deaths in China portrays a virus evolving to adapt to human cells, raising concern about its potential to spark a new global flu pandemic.

The collaborative study, conducted by a group led by Masato Tashiro of the Influenza Virus Research Center, National Institute of Infectious Diseases, and Yoshihiro Kawaoka of the University of Wisconsin-Madison and the University of Tokyo, appears in the current edition (April 11, 2013) of the journal Eurosurveillance. The group examined the genetic sequences of H7N9 isolates from four of the pathogen's human victims as well as samples derived from birds and the environs of a Shanghai market.

"The human isolates, but not the avian and environmental ones, have a protein mutation that allows for efficient growth in human cells and that also allows them to grow at a temperature that corresponds to the upper respiratory tract of humans, which is lower than you find in birds," says Kawaoka, a leading expert on avian influenza.

The findings, drawn from genetic sequences deposited by Chinese researchers into an international database, provide some of the first molecular clues about a worrisome new strain of bird flu, the first human cases of which were reported on March 31 by the Chinese Center for Disease Control and Prevention. So far, the new virus has sickened at least 33 people, killing nine. Although it is too early to predict its potential to cause a pandemic, signs that the virus is adapting to mammalian and, in particular, human hosts are unmistakable, says Kawaoka.

Access to the genetic information in the viruses, he adds, is necessary for understanding how the virus is evolving and for developing a candidate vaccine to prevent infection.

Influenza virus depends on its ability to attach to and commandeer the living cells of its host to replicate and spread efficiently. Avian influenza rarely infects humans, but can sometimes adapt to people, posing a significant risk to human health.

"These viruses possess several characteristic features of mammalian influenza viruses, which likely contribute to their ability to infect humans and raise concerns regarding their pandemic potential," Kawaoka and his colleagues conclude in the Eurosurveillance report.

Kawaoka, a faculty member in the UW-Madison School of Veterinary Medicine who also holds a faculty appointment at the University of Tokyo, explains that the majority of the viruses in the study -- from both humans and birds -- display mutations in the surface protein hemagglutinin, which the pathogen uses to bind to host cells. Those mutations, according to Kawaoka, allowed them to easily infect human cells.

In addition, the isolates from patients contained another mutation that allows the virus to efficiently replicate inside human cells. The same mutation, Kawaoka notes, lets the avian virus thrive in the cooler temperatures of the human upper respiratory system. It is in the cells of the nose and throat that flu typically gains a hold in a mammalian or human host.

Kawaoka and his colleagues also assessed the response of the new strain to drugs used to treat influenza, discovering that one class of commonly used antiviral drugs, ion channel inhibitors which effectively bottle up the virus in the cell, would not be effective; the new strain could be treated with another clinically relevant antiviral drug, oseltamivir.

In addition to Kawaoka and Tashiro, co-authors of the Eurosurveillance report include Tsutomu Kageyama, Seiichiro Fujisaki, Emi Takashita, Hong Xu, Shinya Yamada, Yuko Uchida, Gabriele Neumann and Takehiko Saito. The work was supported by Grants-in-Aid for Pandemic Influenza Research and Grant-in-Aid for Specially Promoted Research from the Ministry of Health, Labour and Welfare, Japan; by the NIAID Center for Research on Influenza Pathogenesis (CRIP, HHSN266200700010C); by a Grant-in-Aid for Specially Promoted Research, by the Japan Initiative for Global Research Network on Infectious Diseases from the Ministry of Education, Culture, Sports, Science, and Technology, Japan; and by ERATO, Japan.

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