Is there a disease that makes us love cats? - Jaap de Roode

譯者: 易帆 余 審譯者: 旻霏 郭

Is there a disease that makes us love cats,

有沒有一種疾病， 會讓我們愛上貓咪呢？

and do you have it?

你有沒有被感染呢？

Maybe,

或許有喔，

and it's more likely than you'd think.

而且比你想的還要嚴重

We're talking about toxoplasmosis,

我們現在要討論的是弓蟲症，

a disease caused by toxoplasma gondii.

一種由弓形蟲引起的疾病。

Like all parasites, toxoplasma lives at the expense of its host,

弓形蟲跟其它寄生蟲一樣， 以吸取宿主的營養為生，

and needs its host to produce offspring.

同時需要借助宿主繁衍下一代。

To do that, toxo orchestrates a brain manipulation scheme

為此，弓形蟲精心策畫了 一種大腦的控制策略，

involving cats,

來控制貓、

their rodent prey,

囓齒類動物、

and virtually all other birds and mammals,

以及大部分的鳥類及哺乳類動物，

including humans.

包含人類。

Documented human infections go as far back as ancient Egypt.

最早有文字記載的人類受感染記錄， 可追溯到古埃及時代。

We found samples in mummies.

我們在木乃伊身上找到了樣本。

Today, about a third of the world's population is infected,

如今，全球大約有 三分之一的人口受到感染。

and most of them never even know it.

而且大多數人對此毫不知情。

In healthy people, symptoms often don't show up at all.

身體健康的人通常不會有感染的徵兆。

When they do, they're mild and flu-like.

就算有，也只是類似感冒的輕微症狀。

But those are just the physical symptoms.

但，那只是身體上的徵兆，

Toxoplasma also nestles into our brains

弓形蟲會進駐我們的腦部，

and meddles with our behavior behind the scenes.

並且會在幕後干涉我們的行為。

To understand why, let's take a look at the parasite's life cycle.

為了要了解為什麼會這樣， 讓我們來看一下寄生蟲的生命周期吧！

While the parasite can multiply in practically any host,

寄生蟲幾乎可以在 任何宿主身上裂變繁洐，

it can only reproduce sexually in the intestines of cats.

但弓形蟲只能在猫的 腸內進行有性繁殖。

The offspring, called oocysts, are shed in the cat's feces.

牠們的幼蟲，也叫卵囊， 會隨猫的糞便排出。

A single cat can shed up to a hundred million oocysts.

一隻猫可以排出高達一億個卵囊。

If another animal, like a mouse, accidentally ingests them,

如果被另外一個動物， 比如老鼠，給意外吞食了，

they'll invade the mouse's tissues and mature to form tissue cysts.

它們就會入侵老鼠的身體組織， 之後會長大形成組織囊腫，

If the mouse gets eaten by a cat,

如果這隻老鼠被貓吃了，

the tissue cysts become active and release offspring

組織囊腫就會活躍起來，

that mate to form new oocysts,

並產下可以 交配繁殖新後代的幼蟲，

completing the cycle.

完成整個生命周期。

But there's a problem.

但有一個問題，

A mouse's natural desire to avoid a cat makes it tough to close this loop.

老鼠怕貓的天性使得 完成這個周期變得困難。

Toxoplasma has a solution for that.

弓蟲症對此有解決辦法。

The parasites invade white blood cells to hitch a ride to the brain

弓形蟲會入侵白血球細胞， 並順道進入腦部。

where they seem to override the innate fear of predators.

在那裏它們似乎可以控制 宿主與生俱來的恐懼。

Infected rodents are more reckless and have slower reaction times.

受感染的囓齒類動物， 動作會變鲁莽、反應會變遲緩。

Strangest of all, they're actually attracted to feline urine,

最奇怪的是，牠們會對猫尿產生好感。

which probably makes them more likely to cross paths with a cat

因此增大了遇到貓的機率，

and help the parasite complete its life cycle.

幫助寄生蟲完成牠的生命循環週期。

How does the parasite pull this off?

這些寄生蟲是怎麼辦到的呢？

Although the exact mechanism isn't known, toxo appears to increase dopamine,

雖然正確的機制還不明確， 但弓蟲症好像會使多巴胺增多，

a brain neurotransmitter that is involved in novelty-seeking behavior.

多巴胺是一種會使人產生好奇行為 的腦部神經傳導素。

Thus, one idea is that toxo tinkers with neurotransmitters,

因此，有一種說法是， 弓形蟲擾亂了神經傳導素，

the chemical signals that modulate emotions.

這種化學反應改變了情緒。

The result?

結果呢？

Fatal attraction.

帶來了致命的吸引力。

But mice aren't the only animals that end up with these parasites,

但是，老鼠並不是唯一 感染這種寄生蟲的動物。

and that's where humans, and all of toxo's other hosts, come in.

人類，和其它弓形蟲的宿主都是。

We can accidentally ingest oocysts in contaminated water,

我們可能會無意中 飲用了受卵囊污染的水源、

or unwashed produce,

或食用未洗乾淨的農產品、

or from playing in sandboxes,

或在沙堆中玩耍、

or cleaning out litter boxes.

或清理垃圾時，都會受到感染。

This is behind the common recommendation that pregnant women not change cat litter.

這也是為什麽一般不建議 懷孕中的女性打掃貓糞便，

Toxo can cause serious birth defects.

因為弓蟲症會引起 嬰兒嚴重的先天缺陷。

We can also get toxo from eating undercooked meat

食用未經煮熟的肉類， 也有機會感染弓蟲症，

from other animals that picked up some oocysts.

接觸身上已有弓形蟲 幼蟲的動物也會，

And it turns out that toxo can mess with our brains, too.

事實證明，弓形蟲也會干擾我們的大腦。

Studies have found connections between toxo and schizophrenia,

研究發現，弓形蟲和精神分裂症、

biopolar disorder,

躁鬱症、

obsessive compulsive disorder,

強迫症和

and aggression.

脾氣暴躁有緊密關係。

It also slows reactions and decreases concentration,

它也會使人反應遲鈍，注意力不集中。

which may be why one study found that people involved in traffic accidents

這或許可以解釋為什麽一項研究發現， 發生交通意外的機率，

were almost three times more likely to have toxoplasma.

有感染弓蟲症的人是沒有患病者的三倍。

So is toxo manipulating our brains as an evolutionary strategy

這麽說來，弓形蟲對我們大腦的操控 是一種進化策略嗎？

to get predatory cats to eat us?

這會讓捕食成性的猫把我們給吃了嗎？

Or are our brains just similar enough to a rodent's

還是因為我們的大腦與 囓齒類動物差不多，

that the same neurological tricks that lure them in catch us in the net, too?

都很容易誘使牠門用同樣的神經官能把戲， 把我們都困在這網中呢？

And is toxo the reason so many people love cats and keep them as pets?

是不是因為弓形蟲，才有那麼多人喜歡猫， 並把牠們當成寵物?

Well, the jury's still out on that one.

這些問題仍然是眾說紛紜，莫衷一是。

Some recent studies even contradict the idea.

一些近期的研究甚至否認這樣的說法。

Regardless, toxoplasma has definitely benefited from humans

無論如何，弓形蟲 確實從人類中獲益匪淺，

to become one of the world's most successful parasites.

從而成為世上最成功的寄生蟲之一。

It's not just our willingness to let cats on our dining room tables

不僅讓我們想跟貓一起在餐桌上進食

or in our beds.

或者一起在床上睡覺。

Raising livestock and building cities which attract rodents

家畜的飼養和城巿的建設， 吸引了囓齒類動物，

has provided billions of new hosts,

為弓形蟲提供了數以萬億計的新宿主。

and you and your cat may be two of them.

而你、和你的猫， 也許就是其中的兩個。