Science：H7N9病毒或可在空气中高效传播

H7N9电镜扫描图，图片由中国疾病与预防中心提供

中国一个病毒学家团队的研究报告发现，近几个月感染132人并导致43人死亡的新型禽流感病毒可在哺乳动物之间通过空气传播，这再次引发了对于这种病毒最终可能在人际传播的担忧。

该研究报告上周四发布在《科学》(Science)杂志的网站上。据发布在《科学》杂志网站上的研究摘要说，研究发现，从中国安徽省一位感染了H7N9禽流感病毒的患者体内分离出来的毒株可在雪貂之间通过飞沫高效传播。

在中国主要病毒学家陈化兰的带领下，研究人员测试了H7N9禽流感病毒多个毒株的传播能力，方法是将三只健康的雪貂放在一个笼子里，旁边的一个笼子里放入三只感染了病毒的雪貂。在大部分情况下，只有一只健康的雪貂感染了病毒，但对于从安徽患者体内分离出来的毒株，三只健康雪貂全部感染。用安徽的毒株重复实验产生的结果相同。

雪貂对流感病毒做出的反应与人类相似，因此常常被用来测试禽流感病毒感染人类及人际传播的可能。

今年3月，中国证实H7N9禽流感病毒首次出现禽类向人类传播的病例，当时中国国有媒体披露说，上海有两人此前一个月感染了H7N9病毒，之后死亡。很快有其他感染者死亡，由于担心可能爆发大范围的疫情，官员们关闭了多个城市的活禽市场，并扑杀了大量禽鸟。

尽管发现有一些“家庭集群式”感染（即多个家庭成员感染）的情况，但卫生主管部门尚未找到证据证明H7N9能够发生人与人之间的传播。如果出现人际传播，这种病毒的危险性就大得多。

但上述新的研究印证了早些时候世界卫生组织(World Health Organization)和中国有关部门发出的警告，他们曾警告说，相比其他任何一种已知的禽流感病毒，H7N9病毒有更高的人际传播的可能。

新华社上周五援引陈化兰的话说，研究结果表明，H7N9病毒株可能只需要几个氨基酸的突变，就会具有高度传播性。

在对上述新的研究的总结中，《科学》杂志指出，研究结果与早些时候美国疾病控制与预防中心(U.S. Centers for Disease Control and Prevention)使用同样的安徽毒株进行的类似研究得出的结果不一致。在美国疾病控制与预防中心的实验中，病毒只传染给了六只健康雪貂中的两只，研究人员由此得出结论，病毒不易通过空气传播。

另外一项由病毒学家河冈义裕(Yoshihiro Kawaoka)主持的研究得出的结果与美国疾病控制与预防中心得出的结果类似。不过研究人员仍得出结论说，H7N9可能给公众健康带来严重威胁。

人感染H7N9禽流感病毒的病例近几个月大幅减少，不过陈化兰在接受新华社采访时警告说，这种病毒仍存在于动物体内。她说，这种病毒在禽类身上并不会出现症状，这一事实意味着，它可以沉默地复制而不引人注意，这增加了它传染给人并获得更多变异成为致病、传播能力更强病毒的机会

英文内容

Since a new bird flu virus began sickening and killing people in China in March, one of the most pressing questions has been whether the virus, H7N9, would easily spread from human to human, possibly kicking off a global pandemic. Fortunately, no convincing signs of such transmission surfaced, and the outbreak—which led affected Chinese cities to close poultry markets and cull birds—seems to have ground to a halt. But three new studies in ferrets show that the virus can spread in the air between mammals, reawakening worries of human-to-human transmission.

Today, a team led by virologist Hualan Chen of China's Harbin Veterinary Research Institute reports online in Science that in experiments with ferrets, an H7N9 virus isolated from a human was what the researchers described as "highly transmissible" by respiratory droplets. In the ferret model, widely regarded as one of the best ways to assess human-to-human transmission, researchers intentionally infect animals in one cage and determine whether the virus spreads to others in an adjacent cage. When Chen and colleagues inoculated three ferrets in one cage with H7N9 virus samples from a person who fell ill with the disease in Anhui province, all three ferrets in an adjacent cage became infected, and the viruses isolated from them matched the ones used in the test. The researchers repeated the experiment and found the same outcome. Two other viral samples from different patients spread to only one of three exposed animals, as did one taken from a bird.

Although the ferret model has its limitations, Chen and co-workers conclude that their findings portend future problems. "Currently, implementation of compulsory control measures in H7N9 virus-positive live poultry markets is preventing further human infections; however, the elimination of the H7N9 virus from nature is a huge and long-term challenge," they write. "Its replication in humans will provide further opportunities for the virus to acquire more mutations and become more virulent and transmissible in the human population."