Why bats don't get sick - Arinjay Banerjee

翻译人员: 校对人员: Helen Chang

如果这只蝙蝠是人类，她就糟糕了。

If this bat were a human, she'd be in deep trouble.

She’s infected with several deadly viruses,

她感染了好几个致命的病毒，

including ones that cause rabies, SARS, and Ebola.

包括了那些会引起狂犬病、非典， 和埃博拉的病毒。

But while her diagnosis would be lethal for other mammals,

虽然她的诊断对 其他哺乳动物来说是致命的，

this winged wonder is totally unfazed.

但对于这个神奇的物种来说 完全没有受到影响。

In fact, she may even spend the next 30 years living

事实上，她甚至可能会在 接下来的30年里继续活着，

as if this were totally normal– because for bats, it is.

仿佛完全正常， 因为对于蝙蝠来说，确实如此。

So what’s protecting her from these dangerous infections?

所以是什么在保护着她， 从而让她免受这些危险的感染呢？

To answer this question, we first need to understand

为了回答这个问题，我们首先需要明白

the relationship between viruses and their hosts.

病毒及其宿主之间的关联。

Every virus has evolved to infect specific species within a class of creatures.

（生物学分类）每一种病毒 都进化成感染

某一纲（Class）中的 特定一种（Species)。

This is why humans are unlikely to be infected by plant viruses,

这就是为什么人类 不太可能被植物病毒感染，

and why bees don’t catch the flu.

和为什么蜜蜂不会感染流感。

However, viruses do sometimes jump across closely related species

但是，病毒有时候会跨越 密切相关的物种。

And because the new host has no established immune defenses,

由于新的宿主没有建立免疫防御系统，

the unknown virus presents a potentially lethal challenge.

未知名的病毒就显现出了 潜在的致命挑战。

This is actually bad news for the virus as well.

这对病毒来说实际上也是个坏消息。

Their ideal host provides a steady stream of resources

理想的宿主提供

源源不断的资源 和接触新宿主的机会，

and comes into contact with new parties to infect—

two criteria that are best met by living hosts.

活宿主恰恰提供这两个机会。

All this to say that successful viruses

也就是说，成功的病毒

don’t typically evolve adaptations that kill their hosts—

通常都不会进化到杀死它们的宿主，

including the viruses that have infected our flying friend.

包括感染了我们飞行朋友的病毒。

The deadly effects of these viruses aren’t caused by the pathogens directly,

这些病毒的致命影响 并不是由病原体直接引起的，

but rather, by their host’s uncontrolled immune response.

而是，由它们的宿主 不受控制的免疫反应。

Infections like Ebola or certain types of flu have evolved

埃博拉病毒或某些类型的感染

已经进化成过度劳损 哺乳动物寄主的免疫系统，

to strain the immune system of their mammalian host

by sending it into overdrive.

使其变得超负荷。

The body sends hordes of white blood cells,

身体发送成群的白细胞，

antibodies and inflammatory molecules to kill the foreign invader.

抗体和炎症分子来杀死外侵者。

But if the infection has progressed to high enough levels,

但如果感染已经进化到够高的级别，

an assault by the immune system can lead to serious tissue damage.

免疫系统的攻击 会导致自身组织的严重损伤。

In particularly virulent cases, this damage can be lethal.

在特别严重的情况下， 这种损害可能致死。

And even when it’s not,

即使未致死，

the site is left vulnerable to secondary infection.

该处也会很容易受到二次感染。

But unlike other mammals,

但与其他哺乳动物不同的是，

bats have been in an evolutionary arms race with these viruses for millennia,

蝙蝠一直在与这些病毒 进行军备竞赛有几千年了，

and they’ve adapted to limit this kind of self-damage.

而且它们已经适应了 限制这种自我伤害。

Their immune system has a very low inflammatory response;

它们的免疫系统 具有非常低的炎症反应；

an adaptation likely developed alongside the other trait

一种适应能力可能 与其他特征并列发展的

that sets them apart from other mammals: self-powered flight.

从而使它们与其他哺乳动物区分开来：

自立飞行。

This energy-intensive process can raise a bat’s body temperature to over 40ºC.

这种能量密集型过程可以将蝙蝠的 体温升高到 40ºC 以上。

Such a high metabolic rate comes at a cost;

如此高的代谢率是有代价的；

flight produces waste molecules called Reactive Oxygen Species

飞行产生称为活性氧物种的废物分子

that damage and break off fragments of DNA.

会损坏和断裂DNA的片段。

In other mammals, this loose DNA

在其他哺乳动动中，这个松散的DNA

would be attacked by the immune system as a foreign invader.

会像外来入侵者一样 受到免疫系统的攻击。

But if bats produce these molecules as often as researchers believe,

但如果蝙蝠经常产生这些分子 就像研究人员想的那样，

they may have evolved a dampened immune response

它们可能已经减弱了免疫系统的反应

to their own damaged DNA.

来损坏它们自己的DNA。

In fact, certain genes associated with sensing broken DNA

事实上，某些与断裂DNA相关的基因

and deploying inflammatory molecules are absent from the bat genome.

和部署炎症分子 是不存在蝙蝠基因组中的。

The result is a controlled low-level inflammatory response

这个结果是一个受约束的 低水平炎症反应，

that allows bats to coexist with the viruses in their systems.

允许蝙蝠与它们系统中的病毒共存。

Even more impressive,

更令人惊讶的是，

bats are able to host these viruses for decades

蝙蝠能够携带这些病毒数十年

without any negative health consequences.

而不会对健康造成任何负面影响。

According to a 2013 study, bats have evolved efficient repair genes

根据2013年的一项研究， 蝙蝠已经进化出有效的修复基因

to counteract the frequent DNA damage they sustain.

来抵消它们所承受的频繁的DNA损伤。

These repair genes may also contribute to their long lives.

这些修复基因可能也会 延长它们的寿命。

Animal chromosomes end with a DNA sequence called a telomere.

动物染色体已一个DNA序列 结束的被称为端粒。

These sequences shorten over time in a process

这些序列在一个过程中 随着时间的推移而缩短

that many believe contributes to cell aging.

许多人认为这会导致细胞老化。

But bat telomeres shorten much more slowly than their mammalian cousins—

但是蝙蝠端粒的缩短速度要比 它们的哺乳动物表亲慢得多—

granting them lifespans as long as 41 years.

赋予它们长达41年的寿命。

Of course, bats aren’t totally invincible to disease,

当然了，蝙蝠并不能 完全战胜所有的疾病，

whether caused by bacteria, unfamiliar viruses, or even fungi.

无论是由细菌、不熟悉的病毒， 还是真菌引起的。

Bat populations have been ravaged by a fungal infection

蝙蝠种群受到过真菌感染的摧残

called white-nose syndrome,

被称为白鼻综合征，

which can fatally disrupt hibernation and deteriorate wing tissue.

就会致命地破坏冬眠系统 并致命地破坏其翅膀的组织。

These conditions prevent bats from performing critical roles

这些状况阻止蝙蝠发挥关键作用，

in their ecosystems, like helping with pollination and seed dispersal,

在它们的生态系统中， 例如帮助授粉和种子传播，

and consuming pests and insects.

以及食用害虫和昆虫。

To protect these animals from harm, and ourselves from infection,

为了保护这些动物免受伤害， 和我们自己免受感染，

humans need to stop encroaching on bat habitats and ecosystems.

人类需要停止侵占蝙蝠的 栖息地和生态系统。

Hopefully, preserving these populations

希望，保护这些群体

will allow scientists to better understand bats’ unique antiviral defense systems.

将使科学家更好地了解 蝙蝠独特的抗病毒防御系统。

And maybe one day, this research will help our own viral immunity take flight.

也许有一天，这项研究将会帮助我们 提高自己的病毒免疫力。