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  • The sun is shining.

    陽光閃耀

  • The birds are singing.

    鳥兒高歌

  • It looks like the start of another lovely day.

    似乎又是美好一天的開始

  • You're walking happily in the park, when, "Ah-choo!"

    你開心地走在公園

  • A passing stranger has expelled mucus and saliva from their mouth and nose.

    突然 "哈啾"

  • You can feel the droplets of moisture land on your skin,

    一個路人噴出鼻涕和口水

  • but what you can't feel are the thousands, or even millions,

    你感覺到皮膚上濕濕的

  • of microscopic germs that have covertly traveled through the air

    但感覺不到成千上萬的微小細菌

  • and onto your clothing, hands and face.

    正經空氣悄悄的

  • As gross as this scenario sounds,

    附著在你的衣服 手和臉上

  • it's actually very common for our bodies to be exposed to disease-causing germs,

    這聽起來有點噁心

  • and most of the time, it's not nearly as obvious.

    卻是身體感染致病細菌的常見途徑

  • Germs are found on almost every surface we come into contact with.

    常常不經意就被傳染到

  • When we talk about germs,

    任何接觸物的表面都有細菌

  • we're actually referring to many different kinds of microscopic organisms,

    我們所說的細菌

  • including bacteria, fungi,

    其實指的是許多不同種的微生物

  • protozoa and viruses.

    包含細菌 真菌 原生動物 病毒

  • But what our germs all have in common is the ability to interact with our bodies

    細菌的共同特點是會和身體互動

  • and change how we feel and function.

    並改變感覺和身體機能

  • Scientists who study infectious diseases have wondered for decades

    數十幾年來 傳染疾病專家始終疑惑

  • why it is that some of these germs are relatively harmless,

    為什麼有的細菌無害

  • while others cause devastating effects and can sometimes be fatal.

    有的卻會嚴重摧毀健康 造成死亡

  • We still haven't solved the entire puzzle,

    我們還沒解開謎團

  • but what we do know is that the harmfulness, or virulence,

    但我們知道有害或致命細菌

  • of a germ is a result of evolution.

    是進化的結果

  • How can it be that the same evolutionary process

    同樣的進化過程怎會產生

  • can produce germs that cause very different levels of harm?

    不同有害程度的細菌呢

  • The answer starts to become clear

    來看看細菌傳染方式就會有答案

  • if we think about a germ's mode of transmission,

    傳染是細菌從一個宿主

  • which is the strategy it uses to get from one host to the next.

    到另一個宿主的途徑

  • A common mode of transmission occurs through the air,

    最常見的是經由空氣傳染

  • like the sneeze you just witnessed,

    像你剛看到的打噴嚏

  • and one germ that uses this method is the rhinovirus,

    鼻病毒就會利用這個方式

  • which replicates in our upper airways,

    在你的上呼吸道複製

  • and is responsible for up to half of all common colds.

    一半以上的普通感冒 都是鼻病毒造成

  • Now, imagine that after the sneeze,

    讓我們想像 經過剛才的噴嚏後

  • one of three hypothetical varieties of rhinovirus,

    三種可能的鼻病毒

  • let's call them "too much," "too little," and "just right,"

    先稱這三種病毒為

  • has been lucky enough to land on you.

    "太多" "太少" 和 "剛剛好"

  • These viruses are hardwired to replicate,

    假設其中一種夠"幸運"跑到你身上

  • but because of genetic differences, they will do so at different rates.

    病毒天生會複製自己

  • "Too much" multiplies very often,

    但因基因不同 複製速率不同

  • making it very successful in the short run.

    "太多" 短時間內 就可大量成功複製病毒

  • However, this success comes at a cost to you, the host.

    但卻使宿主你付出慘痛代價

  • A quickly replicating virus can cause more damage to your body,

    快速複製的病毒嚴重危害健康

  • making cold symptoms more severe.

    使感冒症狀加劇惡化

  • If you're too sick to leave your home,

    若你病到無法起床

  • you don't give the virus any opportunities to jump to a new host.

    病毒沒有任何機會找新宿主

  • And if the disease should kill you,

    若你因此病逝

  • the virus' own life cycle will end along with yours.

    病毒的生命週期也隨你消逝

  • "Too little," on the other hand, multiplies rarely

    另一方面 "太少"複製量不大

  • and causes you little harm in the process.

    因此對健康影響不太大

  • Although this leaves you healthy enough to interact with other potential hosts,

    雖然你能仍健康出門 和潛在宿主接觸

  • the lack of symptoms means you may not sneeze at all,

    但因無症狀 你完全不會打噴涕

  • or if you do, there may be too few viruses in your mucus to infect anyone else.

    即使會 鼻涕裡少數的病毒 也不會影響別人

  • Meanwhile, "just right" has been replicating quickly enough

    "剛剛好"複製的數量快又夠

  • to ensure that you're carrying sufficient amounts of the virus to spread

    讓你帶著足夠的病毒傳播

  • but not so often that you're too sick to get out of bed.

    但不會讓你病到臥床不起

  • And in the end, it's the one that will be most successful

    這種病毒比其他兩種

  • at transmitting itself to new hosts and giving rise to the next generation.

    最容易找到新宿主並繁衍後代

  • This describes what scientists call trade-off hypothesis.

    這是科學家所謂的權衡理論

  • First developed in the early 1980s,

    最先發展於1980年代早期

  • it predicts that germs will evolve to maximize their overall success

    此學說假設細菌藉由

  • by achieving a balance between replicating within a host,

    在宿主體內複製到數量剛好

  • which causes virulence, and transmission to a new host.

    發展最大成功的可能性

  • In the case of the rhinovirus,

    造成新宿主感染病毒

  • the hypothesis predicts that its evolution will favor less virulent forms

    以鼻病毒的例子來說

  • because it relies on close contact to get to its next victim.

    此學說假設鼻病毒的進化會減弱病毒

  • For the rhinovirus, a mobile host is a good host,

    因為需透過近距離傳染

  • and indeed, that is what we see.

    對鼻病毒而言 可到處走的宿主最棒

  • While most people experience a runny nose, coughing and sneezing,

    事實上 這也正是我們所見的

  • the common cold is generally mild and only lasts about a week.

    大多數人流鼻水 感冒 打噴嚏

  • It would be great if the story ended there,

    普通感冒不會太嚴重 最多一星期就好

  • but germs use many other modes of transmission.

    如果事情都那麼簡單就好了

  • For example, the malaria parasite, plasmodium, is transmitted by mosquitoes.

    但細菌會利用許多其他方法傳播

  • Unlike the rhinovirus, it doesn't need us to be up and about,

    例如 瘧疾寄生蟲 瘧原蟲 會經蚊子傳播

  • and may even benefit from harming us

    不像鼻病毒 不需我們站立走動

  • since a sick and immobile person is easier for mosquitoes to bite.

    並會從傷害我們中獲益

  • We would expect germs that depend less on host mobility,

    而臥病在床的病人最容易遭蚊子叮

  • like those transmitted by insects, water or food,

    就如昆蟲 水和食物的細菌感染

  • to cause more severe symptoms.

    可假設這些細菌較不需宿主和他人接觸

  • So, what can we do to reduce the harmfulness of infectious diseases?

    來造成更嚴重症狀

  • Evolutionary biologist Dr. Paul Ewald

    我們可以怎麼做降低感染疾病症狀

  • has suggested that we can actually direct their evolution

    生物進化學家保羅由窩德建議

  • through simple disease-control methods.

    可藉由簡單的疾病控制法主導細菌進化

  • By mosquito-proofing houses, establishing clean water systems,

    如防蚊屋 乾淨水源系統建立

  • or staying home when we get a cold,

    或生病時待在家

  • we can obstruct the transmission strategies of harmful germs

    我們可在身體製造

  • while creating a greater dependence on host mobility.

    更多接觸傳染的細菌同時

  • So, while traditional methods of trying to eradicate germs

    斷絕有害細菌傳染途徑

  • may only breed stronger ones in the long run,

    傳統預防細菌的方法

  • this innovative approach of encouraging them to evolve milder forms

    長久下來可能造成更多強大細菌

  • could be a win-win situation.

    新的方法可使細菌進化較弱

  • (Cough)

    這或許是雙贏方法

  • Well, for the most part.

    咳咳

The sun is shining.

陽光閃耀

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B1 中級 中文 美國腔 TED-Ed 細菌 病毒 宿主 傳染 複製

【TED-Ed】細菌是如何傳播的(為什麼會讓我們生病)?- Yannay Khaikin 和 Nicole Mideo (【TED-Ed】How do germs spread (and why do they make us sick)? - Yannay Khaikin and Nicole Mideo)

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    稲葉白兎 發佈於 2021 年 01 月 14 日
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