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  • There are an estimated...

    估計有...

  • this many individual viruses on Earth.

    地球上這麼多的病毒個體。

  • Luckily, there are only a little over

    幸運的是,只有一點多

  • 1,000 virus strains known to infect humans,

    已知感染人類的1000種病毒株。

  • the majority of which come from other animals.

    其中大部分來自其他動物。

  • They're part of a group called zoonotic diseases,

    它們是人畜共患疾病的一部分。

  • caused by bacteria, viruses, parasites, or fungi.

    由細菌、病毒、寄生蟲或真菌引起;

  • And the one we're all focusing on now

    而我們現在都在關注的是

  • is the virus that causes COVID-19.

    是導致COVID-19的病毒。

  • And new ones can emerge at any time.

    而新的隨時可能出現。

  • Here's what needs to happen

    下面是需要發生的事情

  • for a virus to jump from animals to humans.

    讓病毒從動物跳到人類身上。

  • As a pathogen, the virus' goal

    作為一種病原體,該病毒的目標是

  • is to infect its host and replicate,

    是為了感染宿主並進行復制。

  • because it can't do that on its own.

    因為它自己無法做到這一點。

  • Let's say this pig is the original host of a virus.

    就說這頭豬是病毒的原宿主。

  • He and his buddies form a reservoir,

    他和他的夥伴們組成了一個水庫。

  • a specific population of animals of the same species

    獸類

  • that naturally host a pathogen.

    自然寄生病原體的。

  • Colin Parrish: So, there are millions of viruses out there

    科林・帕裡什。所以,有數以百萬計的病毒有

  • infecting animals. Literally millions.

    感染動物。從字面上看,數以百萬計。

  • I mean, the more we look, the more we find.

    我的意思是,我們看的越多,發現的越多。

  • And most of those viruses

    而這些病毒中的大部分

  • don't infect, you know, other animals.

    不要感染,你知道,其他動物。

  • They have a restricted host range.

    它們的主機範圍有限。

  • Narrator: Most of the time, the virus

    旁白:大多數時候,病毒

  • doesn't affect its original host

    不影響原主機

  • or only mildly affects it.

    或只是輕度影響。

  • So, what's it doing in there?

    那麼,它在裡面做什麼?

  • Suppose that this pig hosts a virus

    假設這頭豬攜帶了一種病毒

  • that primarily infects the gut.

    主要感染腸道的。

  • Viruses tend to attack different parts of the body,

    病毒往往攻擊身體的不同部位。

  • depending on whether they can bind to these guys.

    就看他們能不能和這些人綁定了。

  • Receptors are proteins found along the outside of a cell,

    受體是沿著細胞外部發現的蛋白質。

  • used to communicate with the rest of the body.

    用來與身體其他部位進行交流。

  • But viruses can latch on, too.

    但是,病毒也可以吸附在上面。

  • Cells in a respiratory system may have different receptors

    呼吸系統中的細胞可能有不同的受體。

  • than cells in a digestive tract.

    比消化道的細胞。

  • A virus does its thing by latching onto a host cell,

    病毒是通過吸附在宿主細胞上進行活動的。

  • entering it or injecting bits of itself into it,

    進入其中或將自己的部分注入其中。

  • and then hijacking it.

    然後劫持它。

  • It forces the cell to make copies of the virus,

    它迫使細胞製造病毒的副本。

  • all of which will go on to hijack other host cells.

    都會繼續劫持其他宿主細胞。

  • This will usually kill the host cell.

    這通常會殺死宿主細胞。

  • And if enough of the host cells are infected

    如果有足夠多的宿主細胞被感染的話

  • and make more of the virus,

    並使更多的病毒。

  • the host will contract an infection,

    宿主會受到感染。

  • which, if the body can't fight it off or fights too hard,

    其中,如果身體無法抗衡或抗衡過猛。

  • could lead to severe disease or death.

    可能導致嚴重疾病或死亡。

  • In reservoirs, however, the species has likely evolved

    然而,在水庫中,該物種很可能已經演化出了

  • a resistance to the virus over many generations.

    在許多代人中產生對病毒的抵抗力。

  • This allows a sort of equilibrium;

    這樣就可以達到一種平衡。

  • the immune system controls the infection

    免疫系統控制感染

  • without killing the virus off completely.

    而沒有將病毒徹底殺滅。

  • If the virus jumps, though,

    如果病毒跳動,但。

  • a new host won't have that same, or any, immunity.

    新的主機不會有同樣的,或任何免疫力。

  • That might sound scary, because truthfully

    這可能聽起來很可怕,因為事實上

  • you are constantly being exposed to viruses.

    你不斷地被暴露在病毒中。

  • But only a very small number

    但只有極少數人

  • succeed at infecting a new host species.

    成功感染新的宿主物種。

  • It's called spillover,

    這就是所謂的溢出效應。

  • and there are a series of barriers

    並且有一系列的障礙

  • that a virus must navigate for that to happen.

    病毒必須通過導航才能實現。

  • If it's held up by even one of these,

    如果它被哪怕是其中的一個撐死了。

  • it can be stopped in its tracks.

    它可以被阻止在其軌道上。

  • Simplified, they represent two things:

    簡而言之,它們代表了兩件事。

  • Can the virus get to the new host's cells,

    病毒能否進入新宿主的細胞。

  • and can it bind and enter them?

    並能束縛和進入他們嗎?

  • The more infected pigs there are in one space

    在一個空間裡,感染的豬越多。

  • and the closer they are to people,

    且與人的關係越密切。

  • generally the more chance of spillover.

    一般來說,溢出的機會越多。

  • But the likelihood also has to do with

    但這種可能性還與

  • how the humans are interacting with them.

    人類是如何與它們互動的。

  • Animal viruses are usually transmitted to people

    動物病毒通常會傳染給人

  • in a few ways: contact with excretions,

    在幾個方面:與排洩物接觸。

  • slaughter, bites, contact with tissues,

    屠宰、咬傷、接觸組織;

  • or through an intermediate species

    或通過中間種

  • like mosquitoes or ticks.

    如蚊子或蜱蟲。

  • So places like farms and slaughterhouses

    所以,像農場和屠宰場這樣的地方。

  • and even petting zoos,

    甚至是寵物樂園。

  • where people come in close contact with animals,

    人們與動物親密接觸的地方。

  • have an increased risk of spillover.

    有增加外溢的風險。

  • Proximity alone isn't enough, though.

    不過,光是近距離還不夠。

  • Some of it can be genetic for humans.

    有些可能是人類的遺傳。

  • There's a huge list of genes that have been associated

    有一個龐大的基因列表,已經相關的

  • with different risks of infections,

    具有不同的感染風險。

  • some genes offering resistance to certain infections

    一些基因提供對某些感染的抵抗力

  • and others increasing risk.

    和其他人增加風險。

  • Beyond genes, the virus has to get through

    除了基因之外,病毒還要通過

  • the body's innate immune responses.

    身體的先天免疫反應。

  • Parrish: So, there's two types of immune responses.

    帕裡什所以,有兩種類型的免疫反應。

  • One is the simple adaptive immune responses,

    一是簡單的適應性免疫反應。

  • so those are antibodies and T cells,

    所以這些都是抗體和T細胞。

  • and they generally get stimulated

    他們一般會受到刺激

  • after the infection has already occurred.

    感染已經發生後。

  • The innate responses are the ones that are already present

    先天的反應是已經存在的反應。

  • inside the cell that make a cell or a host,

    細胞內,使細胞或宿主。

  • you know, resistant to the virus.

    你知道,抗病毒。

  • Narrator: Unlike an adaptive response,

    旁白:不像適應性反應

  • an innate one can attempt to fight off any pathogen

    先天的,可以嘗試對抗任何病原體。

  • rather than a specific one.

    而不是一個具體的。

  • Mucus membranes, stomach acids, skin, sentinel cells,

    粘膜、胃酸、皮膚、哨兵細胞。

  • and even just a lack of the right receptors

    甚至只是缺乏正確的受體。

  • can stop a virus from infecting a person.

    可以阻止病毒感染人。

  • So, this is when mutations are really important.

    所以,這時候突變才是真正重要的。

  • A successful spillover usually doesn't happen

    成功的外溢通常不會發生。

  • with the original virus.

    與原始病毒。

  • Parrish: They have to gain some mutations

    帕裡什。他們必須獲得一些突變

  • that allow them to replicate most efficiently,

    使它們能夠最有效地複製。

  • allow them to overcome those host barriers.

    使他們能夠克服這些東道主的障礙。

  • Narrator: A virus that infects

    旁白:感染的病毒

  • the digestive system of the pig

    豬的消化系統

  • might attack respiratory cells in humans.

    可能會攻擊人類的呼吸道細胞。

  • It depends on what receptor the virus is suited for

    這要看病毒適合什麼受體了

  • or mutates to be suited for.

    或變異為適合。

  • Once inside the new host cell,

    一旦進入新的宿主細胞內。

  • an infection will only be successful

    感染才會成功

  • if the virus can replicate.

    如果病毒能夠複製。

  • Typically, infected cells will release interferons,

    通常情況下,受感染的細胞會釋放干擾素。

  • proteins that stop the virus from replicating

    阻止病毒複製的蛋白質

  • within the cell and in nearby cells,

    在細胞內和附近的細胞中。

  • which contain the infection and stop it

    感染,並阻止它

  • from spreading to new cells.

    從傳播到新的細胞。

  • If that doesn't work,

    如果這還不行

  • the adaptive immune system kicks in.

    適應性免疫系統啟動。

  • Your T cells suss out and kill already infected cells

    你的T細胞發現並殺死已經感染的細胞。

  • to stop them from making more new virus,

    以阻止他們製造更多的新病毒。

  • while your white blood cells pump out antibodies

    而你的白細胞則會泵出抗體。

  • specifically tailored to fight this new pathogen.

    專門為對抗這種新的病原體而設計。

  • But because the body has never seen this virus before,

    但因為身體從來沒有見過這種病毒。

  • it can take weeks to produce the right ones.

    它可能需要幾個星期才能生產出合適的。

  • And immunodeficiencies in either type of response

    而任何一種反應類型的免疫缺陷

  • can make it even easier for a virus to take hold.

    可以讓病毒更容易得手。

  • So, if a virus gets through all that,

    所以,如果一個病毒通過所有這些。

  • contact, infection, replication,

    接觸、感染、複製。

  • then it has successfully spilled over.

    那麼它已經成功溢出。

  • But...

    但是...

  • Parrish: The virus has to be able to transmit.

    帕裡什。病毒必須能夠傳播。

  • It has to be able to be shipped from that original person,

    它必須能從那個原人運來。

  • and it has to be able to infect, you know,

    它必須能夠感染,你知道的。

  • at least one or two more additional people

    至少再增加一兩個人

  • so that you can start a chain of transmission.

    以便你可以開始連鎖傳輸。

  • Narrator: A virus infecting two people

    旁白:一種病毒感染了兩個人

  • has double the odds of going on to infect additional people,

    有雙倍的機率去感染更多的人。

  • compared to a virus infecting just one.

    相比於病毒只感染一個。

  • And this can continue until it reaches

    而這種情況可以持續到它達到

  • epidemic and pandemic proportions.

    流行病和大流行病的規模;

  • COVID-19 was certainly not the first zoonotic disease,

    COVID-19當然不是第一個人畜共患病。

  • and it won't be the last.

    而且這不會是最後一次。

  • Viruses don't want to kill their hosts;

    病毒不想殺死它們的宿主。

  • no host means no virus.

    沒有主機就沒有病毒。

  • But new diseases are so dangerous

    但新的疾病是如此危險

  • because humans don't have the same immunity

    因為人類沒有同樣的免疫力。

  • as the virus' reservoir host.

    作為病毒的宿主。

  • And because there are so many,

    因為有這麼多。

  • it's currently not possible to predict

    目前無法預測

  • when or what specific viruses will spill over,

    什麼時候或什麼特定的病毒會溢出來。

  • but we do know the conditions in which spillover can occur.

    但我們確實知道在什麼情況下會發生溢出效應。

  • Parrish: You know, how and where they might occur

    帕裡什。你知道,如何以及在哪裡發生

  • and how we can put in place sort of

    以及我們如何能把在某種程度上

  • better monitoring so that we can catch them early

    更好的監測,以便我們能夠及早發現它們

  • and, as they say, stamp them out

    趕盡殺絕

  • before they get to the point where they become

    在他們變得

  • sort of an out-of-control epidemic.

    某種失控的流行病。

There are an estimated...

估計有...

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