经济学人下载:病毒传播

Which animal SARS-COV-2 leapt from to infect human beings remains unknown.
目前还不清楚究竟是哪种动物将SARS-COV-2传染给了人类。

But the evidence suggests that bats were involved at some point—perhaps not as the immediate source of the virus,
但有证据表明，蝙蝠在某种程度上参与了病毒的传播——也许不是作为病毒的直接来源，

but probably as the reservoir from which it ultimately came.
而是作为病毒的最终来源。

Almost certainly that was true of the virus which caused the original SARS outbreak, in 2002.
几乎可以肯定的是，导致2002年SARS爆发的病毒就是如此。

Though this was transmitted to people by palm civets, they probably caught it from horseshoe bats.
虽然这种病毒是通过椰子猫传染给人类的，但椰子猫可能是被菊头蝠感染的。

MERS, another coronavirus, is similarly suspected of starting in bats, though the immediate source of human infection is camels.
另一种冠状病毒，中东呼吸综合征冠状病毒也被怀疑是由蝙蝠引起的，尽管导致人类感染的直接来源是骆驼。

Bats are also reckoned to be behind the spread of Ebola and Marburg fevers,which are viral infections as well, though not caused by coronaviruses.
蝙蝠也被认为是埃博拉病毒和马尔堡热传播的幕后推手，尽管这两种就并不是由冠状病毒引起的，但它们也是病毒感染。

And vampire bats famously carry another virus, rabies.
吸血蝠还携带着另一种著名的病毒——狂犬病。

The idea that this may not be a coincidence has led people to ask if there is something special about bats
人们认为这可能不是巧合，这一想法这让人们不禁要问，蝙蝠是否有什么特别之处

which encourages the evolution within them of viruses predisposed to jump the species barrier and infect other sorts of animals. At the moment, the evidence is mixed.
促使病毒在它们体内进化，从而有可能跨越物种屏障，感染其他种类的动物。目前，证据比较混乱。

In favour of the idea is an experiment conducted recently by Cara Brook of the University of California, Berkeley, and published in February in eLIFE.
支撑这一想法的是近期由加州大学伯克利分校的Cara Brook进行并于2月发表于《eLIFE》的一项实验。

This suggests a possible mechanism. Some bats have unusual immune systems,
这暗示了一种可能的机制。一些蝙蝠拥有不同寻常的免疫系统，

in which an antiviral process known as the interferon pathway is always active, rather than being switched on in response to infection.
在该系统中，被称为干扰素通路的抗病毒过程始终保持活跃，而不是仅在感染时被激活。

Dr Brook and her colleagues conducted experiments on cells from bats that have this arrangement and on others which do not
Brook博士和她的同事对拥有该种免疫系统以及没有这种系统的蝙蝠的细胞进行实验，

(and also on cells from monkeys, as a control). They concluded that always-on interferon pathways probably do speed up viral evolution.
（作为对照，也对猴子的细胞进行了实验）。他们总结称，永远活跃的干扰素通路可能确实加快了病毒进化。

That would make bats more abundant sources of virulent new viruses than other groups of mammals.
这会让蝙蝠成为比其他哺乳动物更丰富的新病毒来源。

Against the idea, however, is work published this week in the Proceedings of the National Academy of Sciences
然而，反对这种观点的是本周由格拉斯哥大学的Nardus Mollentze和Daniel Streicker

by Nardus Mollentze and Daniel Streicker of the University of Glasgow.
发表于《Proceedings of the National Academy of Sciences》的一项研究。

Dr Mollentze and Dr Streicker found that the number of viruses which have passed to people from 11 orders of mammals and birds
Mollentze和Streicker博士发现，11目哺乳动物和鸟类传给人类的病毒数量

is pretty much proportional to the number of species in each order. Bats are the second-most diverse mammalian order, after rodents.
与每一目中物种的数量成比例。蝙蝠是仅次于啮齿动物的第二大哺乳动物目。

"It is therefore not surprising", Dr Mollentze observes, "that as a group they are associated with a large number of viruses."
Mollentze博士表示：“因此，作为一个群体，它们与大量的病毒有关，这并不奇怪。”

Although bat immune systems do indeed have the unusual features that interested Dr Brook and her colleagues,
虽然，蝙蝠的免疫系统确实有让Brook博士和她的同事感兴趣的特点，

Dr Mollentze and Dr Streicker found no evidence these caused bat-associated viruses to be more numerous
但Mollentze博士和Streicker博士并没有发现证据证明，这导致与蝙蝠相关的病毒

or more prone to infect people than viruses associated with other animal groups.
比与其他动物群体相关的病毒数量更多或更容易感染人类。

This study is in line with work done specifically on coronaviruses by Tracey Goldstein of University of California, Davis.
该研究与加州大学戴维斯分校的Tracey Goldstein针对冠状病毒的专门研究相一致。

In 2017 she and her colleagues published a piece of research in which they had tested for coronaviruses in bats,
2017年，她和她的同事发表了一项研究，她们在非洲、南非和亚洲的20个国家

rodents and primates (including people) in 20 countries in Africa, South America and Asia.
对蝙蝠、啮齿动物和灵长类动物（包括人类）的冠状病毒进行了测试。

Individual bat species normally had between one and five types of coronavirus.
单个蝙蝠种类通常携带冠状病毒类型的数量在1到5种之间。

(For comparison, human beings have seven, including the newly emerged SARS-COV-2.)
（作为比较，人类是7种，包括新出现的SARS-COV-2。）

Scale that up for the 1,400 different species of the animals and it means there are potentially more than 3,000 coronaviruses circulating in bats.
如果扩大到1400种不同种类的动物，那么这就意味着可能有超过3000种冠状病毒在蝙蝠体内流通。

This certainly increases the odds that bats will be responsible for generating a coronavirus dangerous to people. But only because there are lots of them.
这无疑增加了蝙蝠产生对人类危险的冠状病毒的可能性。但这也只是因为它们数量众多。