Why bats don't get sick - Arinjay Banerjee

譯者: Lilian Chiu 審譯者: Amanda Zhu

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

如果這隻蝙蝠是人，

她的麻煩可就大了。

She’s infected with several deadly viruses,

她被數種致命病毒感染，

including ones that cause rabies, SARS, and Ebola.

包括造成狂犬病、SARS， 及伊波拉的病毒。

But while her diagnosis would be lethal for other mammals,

雖然她的診斷結果 對其他哺乳類動物會很致命，

this winged wonder is totally unfazed.

這隻有翅膀的奇蹟生物 卻完全不受影響。

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

事實上，她可能會把 這個狀況當作家常便飯一樣

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

過接下來 30 年的生活——

因為對蝙蝠而言的確就是如此。

So what’s protecting her from these dangerous infections?

所以，是什麼原因讓她能 不受這些危險的感染影響？

To answer this question, we first need to understand

要回答這個問題，我們首先要了解

the relationship between viruses and their hosts.

病毒和其宿主之間的關係。

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

每種病毒都已經演化成會感染

某一綱當中的特定物種。

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

那就是為什麼人類不太可能 被植物病毒感染，

and why bees don’t catch the flu.

以及為什麼蜜蜂不會感冒。

However, viruses do sometimes jump across closely related species

然而，

病毒的確有時會跳到近親物種上。

And because the new host has no established immune defenses,

因為新的宿主尚未建立免疫防禦，

the unknown virus presents a potentially lethal challenge.

未知的病毒會帶來可能致命的危害。

This is actually bad news for the virus as well.

其實這對病毒而言也是壞消息。

Their ideal host provides a steady stream of resources

理想的宿主會持續提供 穩定而源源不絕的資源，

and comes into contact with new parties to infect—

並且會去接觸新的感染對象——

two criteria that are best met by living hosts.

活宿主最好都能達到這兩項標準。

All this to say that successful viruses

這一切的意思就是，成功的病毒

don’t typically evolve adaptations that kill their hosts—

通常不會演化出會造成 宿主死亡的適應性——

including the viruses that have infected our flying friend.

包括感染我們那些蝙蝠 朋友的病毒亦是如此。

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

這些病毒的致命作用 並非由病原體直接造成，

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

而是由其宿主控制不了的 免疫反應所造成。

Infections like Ebola or certain types of flu have evolved

像伊波拉或某些類型的感冒 等感染，都已經演化成

to strain the immune system of their mammalian host

會讓哺乳類宿主的免疫系統 過度操勞而負荷過重。

by sending it into overdrive.

The body sends hordes of white blood cells,

身體會派出大量白血球細胞、 抗體，以及促使發炎的分子，

antibodies and inflammatory molecules to kill the foreign invader.

以殺死外來的入侵者。

But if the infection has progressed to high enough levels,

但，如果已經發展成很高度的感染，

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

免疫系統的攻擊可能會 對組織造成嚴重損傷。

In particularly virulent cases, this damage can be lethal.

在特別劇烈的情況下， 這種損傷可能會致命。

And even when it’s not,

就算不致命，

the site is left vulnerable to secondary infection.

受損傷處也很容易受到二度感染。

But unlike other mammals,

但和其他哺乳類不同的是，

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

數千年來，蝙蝠都一直在 和這些病毒進行演化競賽，

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

牠們已經適應， 能夠限制這種自我損傷。

Their immune system has a very low inflammatory response;

牠們的免疫系統發炎反應非常低，

an adaptation likely developed alongside the other trait

這種適應性可能是和牠們的 另一項特性一起發展出來的，

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

這項特性讓牠們與其他哺乳 有所不同：自供能式飛行。

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

這個需要大量能量的過程，

會讓蝙蝠的體溫 提高到攝氏 40 度以上。

Such a high metabolic rate comes at a cost;

這麼高的代謝率，是有代價的；

flight produces waste molecules called Reactive Oxygen Species

飛行會產生廢棄分子，

稱為活性氧類，

that damage and break off fragments of DNA.

它們會破壞並將 DNA 的 一些片段切斷。

In other mammals, this loose DNA

換作其他哺乳類，這種鬆散的 DNA

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

會被免疫系統視為 外來入侵者而發動攻擊。

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

但如果蝙蝠產生這些分子的頻率 有研究者所相信的那麼頻繁，

they may have evolved a dampened immune response

牠們可能已經演化成 對自己的受損 DNA

to their own damaged DNA.

只會產生較輕的免疫反應。

In fact, certain genes associated with sensing broken DNA

事實上，某些和感測受損 DNA

及部署促炎分子有關的基因

and deploying inflammatory molecules are absent from the bat genome.

都不在蝙蝠的基因組中。

The result is a controlled low-level inflammatory response

結果就是調節得當的低度發炎反應，

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

讓蝙蝠能夠和其系統中的病毒共存。

Even more impressive,

更讓人印象深刻的是，

bats are able to host these viruses for decades

蝙蝠能當這些病毒的宿主數十年

without any negative health consequences.

而不會在健康上有任何負面影響。

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

一篇 2013 年的研究指出，

蝙蝠已經演化出有效的修復基因，

to counteract the frequent DNA damage they sustain.

以對抗牠們經常受到的 DNA 損傷。

These repair genes may also contribute to their long lives.

這些修復基因可能也是 牠們壽命長的原因之一。

Animal chromosomes end with a DNA sequence called a telomere.

動物染色體的末端 是叫做「端粒」的 DNA 序列。

These sequences shorten over time in a process

這類序列會隨時間縮短，

that many believe contributes to cell aging.

許多人相信這個過程 和細胞老化有關。

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

但蝙蝠的端粒縮短速度 比其他哺乳類要慢很多——

granting them lifespans as long as 41 years.

讓牠們的壽命能長達 41 年。

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

當然，蝙蝠並不是完全不怕疾病，

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

能讓牠們致病有細菌、 陌生病毒，甚至黴菌。

Bat populations have been ravaged by a fungal infection

蝙蝠的數量曾經被一種

叫做白鼻症的黴菌感染而銳減，

called white-nose syndrome,

which can fatally disrupt hibernation and deteriorate wing tissue.

這種疾病會打斷冬眠、 讓翅膀組織退化，最後致命。

These conditions prevent bats from performing critical roles

這些疾病讓蝙蝠無法扮演 牠們在生態系統中的重要角色，

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

比如協助授粉、傳播種子，

and consuming pests and insects.

以及吃掉危害作物的動物和昆蟲。

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

為了保護這些動物不受傷害 以及保護我們自己不受感染，

humans need to stop encroaching on bat habitats and ecosystems.

人類必須要停止侵犯

蝙蝠的棲息地和生態系統。

Hopefully, preserving these populations

希望做好蝙蝠族群的保育，

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

能讓科學家更了解

蝙蝠獨特的抗病毒防禦系統。

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

也許有一天，

這些研究也能協助 我們自己對病毒免疫力起飛。