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

翻译人员: Wanting Zhong 校对人员: Ameerah Arjanee

A new virus emerges and spreads like wildfire.

一种新型病毒已经出现， 并如野火般迅速传播。

In order to contain it,

为了控制住它，

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

研究者先必须收集数据 来确定谁受到了感染。

Two main viral testing techniques are critical:

两种病毒检测技术至关重要：

one tells you if you have the virus

一种判断你是否携带病毒，

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

另一种显示你是否曾受到过感染。

So, how exactly do these tests work?

那么，这些检测的原理是什么？

PCR, or polymerase chain reaction testing,

PCR，也就是 聚合酶链式反应，

targets the virus’s genetic material in the body

一种针对人体内病毒的 遗传物质进行检测手段，

and is used to diagnose someone who is currently infected.

被用来诊断目前已被感染的患者。

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

但病毒遗传物质的含量 可能微乎其微，

that actually detecting it is difficult.

导致实际检测非常困难。

This is where PCR comes in:

这就是 PCR 派上用场的地方：

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

它被广泛运用于 大量扩增遗传信息，

that it can be readily observed.

使其能被轻松地检测出来。

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

要想为前所未有的新病毒 开发 PCR 检测，

researchers first sequence its genetic material, or genome,

研究者首先要对其遗传物质， 即基因组，进行测序，

and identify regions that are unique to that specific virus.

并且识别出 这种病毒独有的基因片段。

PCR then targets these particular segments.

PCR 随后就能针对 这些特定片段进行扩增。

A PCR test begins by collecting a sample:

PCR 检测从采集样本开始：

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

例如用于肝炎病毒检测的血液、 用于脊髓灰质炎病毒检测的粪便，

and samples from the nose or throat for coronaviruses.

或是用于冠状病毒检测 的鼻腔或咽喉拭子。

The sample is taken to a central laboratory

样本会被带至中心实验室，

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

在那里进行 PCR 来检测 病毒基因组的存在。

Genetic information can be encoded via DNA or RNA.

遗传信息可以通过 DNA 或 RNA 进行编码。

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

例如，人类乳头瘤病毒（HPV） 用 DNA 编码，

而导致新冠肺炎的 SARS-CoV-2 则用 RNA 编码。

uses RNA.

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

在进行 PCR 操作之前， 如果还存在病毒的 RNA，

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

则必须先将其逆转录， 合成一股互补 DNA，

Researchers then run the PCR.

然后再进行 PCR 检测。

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

如果样品中含有病毒， 它的独特基因编码区域

will be identified by complementary primers and copied by enzymes.

会被互补的引物识别， 并被酶复制。

One strand of DNA becomes hundreds of millions,

一股 DNA 变成数亿股，

which are detected using probes marked with fluorescent dye.

并被用荧光染料标记的 探针检测出来。

If the PCR machine senses fluorescence,

如果 PCR 仪器检测到荧光，

the sample has tested positive for the virus,

样本对该病毒的检测就呈阳性，

meaning the individual is infected.

即被检个体为感染者。

Immunoassays, on the other hand,

另一种方法，免疫分析，

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

则通过发掘免疫系统对病毒的记忆，

showing if someone has previously been infected.

来显示某人之前是否曾受过感染。

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

它的原理是检测 免疫系统在感染时生成的

针对特定病毒的抗体。

during infection.

These are specialized classes of proteins

抗体是一类特化的蛋白质，

that identify and fight foreign substances, like viruses.

能识别并抵抗外来物质， 例如病毒。

Immunoassays may detect IgG antibodies, the most abundant class,

免疫分析可以检测 IgG 抗体， 含量最充足的一类抗体，

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

以及 IgM 抗体，在响应新感染时 最先生成的抗体。

The presence of IgM antibodies suggests a recent infection,

IgM 抗体的存在 意味着最近有受到过感染，

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

但因为身体至少需要一周 才能产生可检测的抗体量，

they’re unreliable in diagnosing current infections.

IgM 检测在用于诊断 目前的感染时并不可靠。

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

而 IgG 抗体在感染后的 较长时间内仍会在体内循环；

their presence usually indicates that someone was exposed and recovered.

它们的存在通常表明 某人曾被感染，然后痊愈了。

Before the immunoassay,

在免疫分析前，

health professionals draw blood from an individual.

医护人员会为被检个体抽血，

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

然后将血样和一部份 目标病毒进行接触。

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

如果被检者在过去 确实接触过这种病毒，

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

那体内的特异性抗体 会在检测中与病毒结合。

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

这个反应会产生颜色变化， 表明样品检测呈阳性，

and that the individual has been exposed to the virus.

并且被检者曾接触过病毒。

Immunoassays are especially important

在回溯诊断

曾被感染却未经检测的人群时，

when it comes to retroactively diagnosing people

who were infected but went untested.

免疫分析就十分重要。

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

已经对病毒产生免疫的人 有令人振奋的潜力：

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

某些情况下，他们的血浆 可以用来治疗

in people who are currently fighting it.

正在与病毒奋战的患者。

PCR and immunoassays are always in the process

PCR 和免疫分析的精确性和效率

of becoming more accurate and efficient.

一直在不断提升。

For example,

比如，

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

PCR 技术的革新 已经带来了独立检测设备，

that relay results within one hour.

能在一个小时内得出结果。

Digital PCR, which quantifies individual pieces of target DNA,

数字 PCR 能对 目标 DNA 的个别片段进行定量，

shows promise in further boosting accuracy.

在进一步提高精确性方面前景可观。

And although immunoassays are difficult to develop quickly,

虽然免疫分析难以快速开发，

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

但新加坡的研究者得以在 新冠疫情被宣布为大流行前，

even before COVID-19 was declared a pandemic.

就研发了出针对新冠病毒的 免疫分析手段。

These tests— along with the scientists who develop them

这些检测—— 以及开发它们的科学家

and the health professionals who administer them—

和进行检测的医疗人员——

are absolutely essential.

都是至关重要的。

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

如果可以尽早投入使用， 它们就能拯救数以百万计的生命。