【翻译】寨卡病毒：不再是个谜

The Zika virus

A mystery no more

 

寨卡病毒

不再是个迷

 

Scientists have learned a great deal about Zika since the outbreak began. Now for the task of stopping it

Sep 17th 2016 | From the print edition

 

自寨卡（Zika）爆发以来，科学家对它已掌握了足够多的资料。现在是时候终结它了。

 

《经济学人》2016.9.17

 

A YEAR ago, most people would have drawn a blank if asked about Zika. Since then, an outbreak of the mosquito-borne virus that began in early 2015 in Brazil has spread to more than 60 countries in the Americas, Africa, Asia and the Pacific islands (see chart). A study published on September 1st in the Lancetestimates that 2.6 billion people live in areas to which Zika could eventually spread. 

一年之前，提到寨卡的时候大多数人一无所知。而从那以后，这个2015年于巴西开始爆发的蚊传播病毒已在美洲、非洲、亚洲和太平洋诸岛中超过60个国家传播。9月1号发表于《柳叶刀》（Lancet）的一篇研究估计，有26亿人居住在寨卡病毒的可传播范围内。

 

At first, scientists knew little more than anyone else. Zika is not new; the virus was first isolated in Africa in 1947. But it was obscure, and therefore little studied. Only during the present outbreak did it become clear that infection among pregnant women was associated with birth defects and neurological problems in babies. But there has been much progress, and scientists now know far more about the disease than they did when the outbreak began.

最初，科学家对这种病毒也知之甚少。寨卡并不是新出现的病毒，它早在1947年于非洲被分离出来。它很不起眼，因此对它鲜有研究。一直到如今病毒蔓延时，人们才知道生育缺陷、幼儿神经问题和孕妇感染此种病毒有关系。不过现在对此病毒的研究已大有进展，科学家对它也比在爆发初期知道的多的多。

 

Start with transmission. The vast majority of Zika infections occur through the bite of Aedes aegypti, a mosquito common in tropical climates and especially in cities. Another species, A. albopictus, which thrives in cooler climes, may also be able to transmit the bug, though possibly not as efficiently. Unusually for a mosquito-borne virus, Zika can also be transmitted sexually (the first case of transmission in the United States occurred this way). Studies are under way to find out how long after infection that remains possible, but traces of the virus’s genetic code have been found in semen six months after the onset of symptoms. Infection through blood transfusion has been confirmed as well. The virus has also turned up in urine, tears and saliva, though that does not necessarily mean that it can spread through them.

从传播开始说起。绝大部分的寨卡感染源于埃及伊蚊（Aedes aegypti），这种蚊子一般栖息于热带气候，尤其是城市中。另一种白纹伊蚊（albopictus）生存于较冷的气候中，或许也能传播病毒，虽然其效率可能没有前者高。不同于一般的蚊媒病毒，寨卡同时也能通过性接触传播（美国的第一例感染是以此种方式）。当下进行中的研究志在发现在感染后过久病毒仍能传播。在病人出现感染症状的六个月后，在其精液中发现了病毒的遗传信息痕迹。现在也已确定病毒能通过血液传播。病毒也在尿液、泪液和唾液中被发现，虽然这并不必然表示病毒能通过它们传播。

 

The health effects of the virus are becoming clearer too. Something like four in five Zika infections cause no symptoms. The rest usually pass with only mild discomfort, including a rash and red eyes. Occasionally, infected people develop Guillain-Barré syndrome, a condition in which the immune system goes awry, causing weakened muscles and temporary paralysis. Death is rare, but some sufferers spend weeks hooked to a breathing machine.

这种病毒对健康的影响也越来越显而易见了。例如五分之四的感染不导致任何症状。其余的通常仅仅伴有轻微的不适，包括皮疹和红眼病。偶尔也有病例出现格林·巴利综合征（Guillain-Barré syndrome），这是一种免疫系统紊乱的病症，能导致肌无力和瘫痪。它通常是不致死的，但也有一些患者要使用数周的呼吸机。

 

Infection is also dangerous if it occurs during pregnancy: in perhaps 1-2% of cases the virus attacks the brain tissue of the fetus. That causes microcephaly, a condition characterised by an abnormally small head, a result of the skull collapsing around the shrunken brain. Babies who escape that fate may suffer other Zika-related damage, including eyesight and hearing loss. Scans of apparently healthy babies born to infected mothers sometimes show brain abnormalities, though it is too early to know whether these will lead to developmental problems later in life. And there are worries, as yet unresolved, about the neurological implications in adults, too.

如果感染发生在妊娠期就很危险：在大约1-2%的案例中病毒会攻击胎儿的脑组织。这会导致小头症（microcephaly），一种由脑萎缩造成的颅骨塌陷导致的病症。躲过此劫的婴儿也许还会承受其他寨卡造成的伤害，包括视力和听力丧失。在对受感染的母亲生下的看起来健康的婴儿的检查中发现，他们有时会表现出大脑畸形，不过还暂时不能断定这是否会在后来造成发展性病症。当然也不乏对成人的神经系统在感染中可能受到牵连的担忧，这是一个悬而未决的问题。

 

Then there is the question of tracking and diagnosis. Working out just how far Zika has spread within a country is tricky. A common test works by testing for antibodies, specialised proteins produced by the immune system that are designed to disable the virus. But it cannot distinguish easily between antibodies for Zika and those for dengue fever, another mosquito-borne illness, which is related to Zika and often occurs in the same sorts of places. That may turn out to be a good thing: antibodies against dengue may provide some defence against Zika. But it muddles attempts to track the disease, and to predict how it might spread.

另外还有对病症的追踪和诊断的问题。仅仅确定一个国家内寨卡传播了多大范围就是一个比较棘手的问题。普遍的方法是对抗体进行测试，这是一种由对抗病毒的免疫系统生成的特殊蛋白质。但此种抗体和对抗登革热（Dengue Fever）的抗体不易区分。登革热是另一种蚊媒病症，和寨卡有关而且经常和寨卡出现在同类地区。这也许会是件好事：针对登革热的抗体可能对寨卡有部分抵抗作用。但这会扰乱追踪病毒、预测病毒如何传播的尝试。

 

Two open questions are whether a Zika infection confers lasting immunity to the virus, and how strains from the two known lineages—one African and one Asian—might interact. There are reasons to worry: an initial infection with one of the four strains of dengue is usually harmless, but subsequent infection with another strain can be fatal.

寨卡感染是否能带来对此病毒的持续免疫能力，以及来自非洲和亚洲的两种病毒株会如何相互影响，这是两个尚无定论的问题。这也是值得我们担心的：登革热的四种病毒株之一造成的最初感染一般是无害的，但若随后感染另一病毒株则可能会致死。

 

An ounce of prevention

一些预防

（An ounce of prevention is worth a pound of cure  --Benjamin Franklin 语出富兰克林，预防胜于治疗—译注）

Official advice continues to evolve with the stream of new findings. Preventing mosquito bites is the main line of defence. The World Health Organisation prescribes condoms or sexual abstinence for at least six months for those returning from areas where Zika is spreading. Several countries have begun screening blood donors.

官方建议是随着不断涌现的新发现而改变的。防止蚊虫叮咬是主要预防手段。世界卫生组织要求，从寨卡传播地区离开的人在性交时要佩戴安全套，或保持至少6个月的禁欲。一些国家已开始对献血者进行甄别。

 

The most encouraging news is on the vaccine front. Several are in early-stage trials. Two—one developed by the National Institutes of Health in America, and the other by Inovio Pharmaceuticals, a private firm—use a new technology called “DNA vaccination”. Traditional vaccines use either dead viruses or weakened live ones to provoke an immune response. DNA vaccines introduce snippets of the viral genome into the patient’s cells, relying on the cells themselves to produce viral proteins that are then recognised by the immune system. DNA is much easier to handle than weakened or dead viruses; and by focusing on genetic sequences common to different variants, a vaccine may offer protection against several strains of the virus. If all goes well, large-scale trials could begin early next year, with results by mid-2018.

最振奋人心的消息是关于疫苗的。一些疫苗已处于早期试用阶段。其中之一由美国国立卫生研究院研发，另一种由一家私人公司—Inovio制药研发，使用了“DNA接种“（DNA vaccination）新技术。传统的疫苗使用失活病毒或减毒活病毒来激起免疫反应。DNA疫苗使病毒的基因组片段进入宿主细胞，依靠细胞自身产生病毒蛋白，而后被免疫系统识别。DNA比减毒或失活病毒更易控制，另外，针对基因序列的相同部分和不同变体的研究也许能给一种疫苗带来抵抗多种病毒株的效果。如果进展顺利，明年年初即可进行大规模试验，而在2018年中可得到结果。

 

By contrast, efforts to cull mosquitoes have been less successful. Aedes aegypti is a hardy creature, happy to breed in water pools as tiny as a bottle cap; it has also learned to live indoors, in nooks where outdoor spraying cannot reach it.

然而，消灭蚊虫的努力就没有那么成功了。埃及伊蚊是个强健的物种，乐于在瓶盖这么小的水洼里繁殖。它也学会了在室内生活，生活在室外除蚊喷雾无法到达的角落里。

 

So the hunt is on for other ways to limit mosquito numbers. One is to unleash mosquitoes pre-infected with Wolbachia, a bacterium that impairs their ability to transmit Zika, and makes males sterile. The hope is those males will mate with wild females but produce no offspring, shrinking the size of the next generation. An alternative is to release mosquitoes sterilised with radiation, though this may make them less appealing suitors. Oxitec, a British firm, has developed genetically modified Aedes aegypti whose offspring die before reaching adulthood; in trials, releasing them into the wild has cut mosquito counts by 90%.

所以要使用其他方式捕杀蚊虫来限制其数量。其一是释放使之预先感染了沃尔巴克氏体（Wolbachia）的蚊子，这种细菌可削弱它们传播寨卡的能力，而且可使雄性不育。此举旨在使雄性蚊子和野生雌蚊交配但不产生后代，以此削减蚊子下一代的数量。另一替代方法是投放使用射线绝育后的蚊子，虽然这可能使它们对雌蚊的吸引力减弱。英国公司Oxitec已培育出基因改造过的埃及伊蚊，他们的后代会在成年前死去。在试验中，投放此种蚊子能使野外蚊子数量降低90%。

 

The trouble with such ideas is that they give evolution a powerful incentive to select its way around the problem. Over time, that could make them less effective. One option that might avoid that problem is a “gene drive”, a new technique that tweaks genomes in a way that ensures that the modified, damaging traits are inherited by all of a mosquito’s offspring. Gene drives are highly controversial: if they work, they could give humans the power to wipe out—with minimal effort—any species that engages in sexual reproduction. They are also experimental and confined to labs; no one knows how effective they would be in the wild. Last week the Bill and Melinda Gates Foundation, a charity, announced it would boost its funding of gene-drive research to $75m. That will speed up the work—and the debate about deliberately wiping out a species.

这些方法的弊端在于，它们极大地促进了蚊虫朝规避这些手段的方向进化，假以时日这些方法就会不再那么奏效。规避此问题的方法之一是“基因驱动”（gene drive），即以某种方式对基因组稍作修改，从而确保修改过的、具有破坏性的性状能被一只蚊子的所有后代继承的新技术。基因驱动具有很大争议，如果它行之有效，那么就能给人类来带来以极小代价灭绝任何一个有性生殖物种的能力。不过它还是实验性的，只在实验室中进行，没人知道在野外有多大效果。上周，一个慈善组织，比尔和梅琳达·盖茨基金会（Bill and Melinda Gates Foundation）宣布对基因驱动研究的基金支持提高到7500万美元。这会加速此技术的研究，也会激化关于蓄意消灭物种问题的争议。

 

英文原文摘自《经济学人》杂志，仅作学习交流之用，版权归原作者所有。