How do you know if you have a virus? - Cella Wright

譯者: Lilian Chiu 審譯者: Carol Wang

A new virus emerges and spreads like wildfire.

有一種新型病毒出現， 且像野火般散播出去。

In order to contain it,

為了控制住疫情，

researchers must first collect data about who’s been infected.

研究員首先必須要收集資料， 了解受感染的是哪些人。

Two main viral testing techniques are critical:

有兩種主要的病毒檢測技術非常重要：

one tells you if you have the virus

一種能判斷你目前 身上是否有病毒，

and the other shows if you’ve already had it.

另一種則能顯示 你是否曾經染上病毒。

So, how exactly do these tests work?

這些檢測的原理是什麼？

PCR, or polymerase chain reaction testing,

聚合酶連鎖反應（PCR）檢測

targets the virus’s genetic material in the body

針對病毒在人體內的遺傳物質，

and is used to diagnose someone who is currently infected.

可用來診斷受測者 目前是否受到感染。

Yet, this genetic material may be present in such imperceptible amounts

但，這種遺傳物質的量 可能非常微小，

that actually detecting it is difficult.

微小到很難偵測到。

This is where PCR comes in:

此時 PCR 就派上用場了：

it’s widely used to amplify genetic information to large enough quantities

PCR 被廣泛應用在

將遺傳資訊放大到 可以很容易觀察到的程度。

that it can be readily observed.

To develop a PCR test for a never-before-seen virus,

若要針對前所未見的病毒 來開發 PCR 檢測，

researchers first sequence its genetic material, or genome,

研究員首先得要對該病毒的 遺傳物質即基因組做定序，

and identify regions that are unique to that specific virus.

找出該病毒與其他 病毒不同的區域。

PCR then targets these particular segments.

接著，PCR 會把目標放在 這些特定區域上。

A PCR test begins by collecting a sample:

PCR 檢測一開始要先收集樣本：

this can be blood for hepatitis viruses, feces for poliovirus,

肝炎病毒可以用血液樣本， 小兒麻痺病毒可以用糞便樣本，

and samples from the nose or throat for coronaviruses.

冠狀病毒可以用取自 鼻子或喉嚨的樣本。

The sample is taken to a central laboratory

樣本會被送到中央實驗室，

where PCR is performed to test for the presence of the virus’ genome.

在那裡進行 PCR，來檢測 是否有該病毒的基因組。

Genetic information can be encoded via DNA or RNA.

可以透過 DNA 或 RNA 來做基因資訊的編碼。

HPV, for example, uses DNA, while SARS-CoV-2, the cause of COVID-19,

如，人類乳突病毒用的是 DNA，

而引起 2019 冠狀病毒病的 SARS-CoV-2 則用 RNA。

uses RNA.

Before running the PCR, the viral RNA— if present—

在進行 PCR 之前，病毒的 RNA ——如果有的話——

must be reverse transcribed to make a strand of complementary DNA.

必須要經過反轉錄， 來製造一股互補 DNA。

Researchers then run the PCR.

接著，研究員會進行 PCR。

If the virus is present in the sample, its unique regions of genetic code

如果樣本中有病毒， 其獨特的遺傳編碼區域

will be identified by complementary primers and copied by enzymes.

就會被互補的引子 辨視出來，並被酵素複製。

One strand of DNA becomes hundreds of millions,

一股 DNA 就會變成數億股，

which are detected using probes marked with fluorescent dye.

會被帶有螢光標記 染料的探測器偵測到。

If the PCR machine senses fluorescence,

如果 PCR 機器感測到螢光染料，

the sample has tested positive for the virus,

樣本對該病毒的 檢測結果就是陽性，

meaning the individual is infected.

意即受測者受到感染。

Immunoassays, on the other hand,

另一方面，免疫分析檢測的是 免疫系統對病毒的記憶，

tap into the immune system’s memory of the virus,

showing if someone has previously been infected.

顯示受測者是否曾經被感染過。

They work by targeting virus-specific antibodies generated by the immune system

原理是，受到感染時，

免疫系統會針對不同病毒 產生出不同抗體。

during infection.

These are specialized classes of proteins

這類抗體是有專門功能的蛋白質，

that identify and fight foreign substances, like viruses.

能夠辨視出、對抗 外來物質，如病毒。

Immunoassays may detect IgG antibodies, the most abundant class,

免疫分析可偵測到 IgG 抗體， 這類抗體是最充足的抗體，

and IgM antibodies, the type that’s first produced in response to a new infection.

及 IgM 抗體，在因應新感染時 最先產生出來的抗體。

The presence of IgM antibodies suggests a recent infection,

若有發現 IgM 抗體， 就表示近期有受過感染，

but since it can take the body over a week to produce a detectable amount,

但因為身體至少要一週才能 產生出偵測得到的抗體量，

they’re unreliable in diagnosing current infections.

若想診斷目前是否有受到感染， 這種方式並不可靠。

Meanwhile, IgG antibodies circulate for an extended period after infection;

同時，在感染過後，IgG 抗體 還會額外在體內循環一段時間；

their presence usually indicates that someone was exposed and recovered.

發現這種抗體通常是表示 受測者曾經接觸病毒且已復原。

Before the immunoassay,

在進行免疫分析之前，

health professionals draw blood from an individual.

健康專業人士會幫受測者抽血。

This sample then comes into contact with a portion of the virus of interest.

接著讓血液樣本和一部分 要檢測的目標病毒做接觸。

If the body has, in fact, been exposed to the virus in the past,

如果受測者過去曾經 有接觸過這種病毒，

the body’s virus-specific antibodies will bind to it during the test.

在檢測時，體內針對這種病毒 產生的抗體就會和病毒結合。

This reaction produces a change in color, indicating that the sample tested positive

這種反應會造成顏色改變， 表示樣本檢測的結果為陽性，

and that the individual has been exposed to the virus.

也就是該受測者曾經接觸過病毒。

Immunoassays are especially important

免疫分析特別重要的應用是：

when it comes to retroactively diagnosing people

回溯診斷曾經受過感染

who were infected but went untested.

卻沒有被檢測出來的人。

And there’s exciting potential for those who have developed immunity to a virus:

如果有人已經有可以抵抗病毒的 免疫力，那是很讓人振奮的：

in some cases, their blood plasma could be used as treatment

在某些情況下，可以把他們的血漿

in people who are currently fighting it.

拿來治療還在和病毒奮戰的人。

PCR and immunoassays are always in the process

PCR 和免疫分析的準確度

of becoming more accurate and efficient.

和效率一直都不斷在提升中。

For example,

比如，在 PCR 的創新上，

innovations in PCR have led to the use of self-contained testing devices

已經出現了獨立檢測裝置，

that relay results within one hour.

可以在一小時內得到結果。

Digital PCR, which quantifies individual pieces of target DNA,

數位 PCR 可以量化 目標 DNA 的個別片段，

shows promise in further boosting accuracy.

未來有很好的前景， 能將正確率大大提升。

And although immunoassays are difficult to develop quickly,

雖然免疫分析的發展 很難快得起來，

researchers in Singapore were able to create one for SARS-CoV-2

但新加坡的研究員已經 能夠針對新型冠狀病毒

even before COVID-19 was declared a pandemic.

建造出免疫分析，且時間還是 在宣佈新型冠狀病毒大流行之前。

These tests— along with the scientists who develop them

這些檢測—— 及開發它們的科學家，

and the health professionals who administer them—

和管理測試的健康專業人士——

are absolutely essential.

都是非常重要的。

And when deployed early, they can save millions of lives.

如果能及早拿來實際應用， 數百萬人可能會因此得救。