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A new virus emerges and spreads like wildfire. In order to contain it, researchers must first collect data about who's been infected.
一种新型病毒已经出现，并如野火般迅速传播。为了控制住它，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: one tells you if you have the virus and the other shows if you've already had it.
两种病毒检测技术至关重要：一种判断你是否携带病毒，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, targets the virus's genetic material in the body and is used to diagnose someone who is currently infected.
PCR，也就是聚合酶链式反应，一种针对人体内病毒的遗传物质进行检测手段，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 that actually detecting it is difficult.
但病毒遗传物质的含量可能微乎其微，导致实际检测非常困难。
This is where PCR comes in: it's widely used to amplify genetic information to large enough quantities that it can be readily observed.
这就是PCR派上用场的地方：它被广泛运用于大量扩增遗传信息，使其能被轻松地检测出来。
To develop a PCR test for a never-before-seen virus, researchers first sequence its genetic material, or genome, and identify regions that are unique to that specific virus.
要想为前所未有的新病毒开发PCR检测，研究者首先要对其遗传物质，即基因组，进行测序，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: this can be blood for hepatitis viruses, feces for poliovirus, and samples from the nose or throat for coronaviruses.
PCR检测从采集样本开始：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，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 where PCR is performed to test for the presence of the virus' genome.
样本会被带至中心实验室，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, uses RNA.
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。
Before running the PCR, the viral RNA -- if present -- must be reverse transcribed to make a strand of complementary DNA. Researchers then run the PCR.
在进行PCR操作之前，如果还存在病毒的RNA，则必须先将其逆转录，合成一股互补DNA，然后再进行PCR检测。
If the virus is present in the sample, its unique regions of genetic code will be identified by complementary primers and copied by enzymes.
如果样品中含有病毒，它的独特基因编码区域会被互补的引物识别，并被酶复制。
One strand of DNA becomes hundreds of millions, which are detected using probes marked with fluorescent dye.
一股DNA变成数亿股，并被用荧光染料标记的探针检测出来。
If the PCR machine senses fluorescence, the sample has tested positive for the virus, meaning the individual is infected.
如果PCR仪器检测到荧光，样本对该病毒的检测就呈阳性，即被检个体为感染者。
Immunoassays, on the other hand, tap into the immune system's memory of the virus, showing if someone has previously been infected.
另一种方法，免疫分析，则通过发掘免疫系统对病毒的记忆，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 during infection.
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。
These are specialized classes of proteins that identify and fight foreign substances, like viruses.
抗体是一类特化的蛋白质，能识别并抵抗外来物质，例如病毒。
Immunoassays may detect IgG antibodies, the most abundant class, and IgM antibodies, the type that's first produced in response to a new infection.
免疫分析可以检测IgG抗体，含量最充足的一类抗体，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, they're unreliable in diagnosing current infections.
但因为身体至少需要一周才能产生可检测的抗体量，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; their presence usually indicates that someone was exposed and recovered.
而IgG抗体在感染后的较长时间内仍会在体内循环；它们的存在通常表明某人曾被感染，然后痊愈了。
Before the immunoassay, health professionals draw blood from an individual.
在免疫分析前，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, the body's virus-specific antibodies will bind to it during the test.
如果被检者在过去确实接触过这种病毒，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 and that the individual has been exposed to the virus.
这个反应会产生颜色变化，表明样品检测呈阳性，并且被检者曾接触过病毒。
Immunoassays are especially important when it comes to retroactively diagnosing people who were infected but went untested.
在回溯诊断曾被感染却未经检测的人群时，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 in people who are currently fighting it.
某些情况下，他们的血浆可以用来治疗正在与病毒奋战的患者。
PCR and immunoassays are always in the process of becoming more accurate and efficient.
PCR和免疫分析的精确性和效率一直在不断提升。
For example, innovations in PCR have led to the use of self-contained testing devices that relay results within one hour.
比如，PCR技术的革新已经带来了独立检测设备，能在一个小时内得出结果。
Digital PCR, which quantifies individual pieces of target DNA, shows promise in further boosting accuracy.
数字PCR能对目标DNA的个别片段进行定量，在进一步提高精确性方面前景可观。
And although immunoassays are difficult to develop quickly, researchers in Singapore were able to create one for SARS-CoV-2 even before COVID-19 was declared a pandemic.
虽然免疫分析难以快速开发，但新加坡的研究者得以在新冠疫情被宣布为大流行前，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 and the health professionals who administer them -- are absolutely essential.
这些检测--以及开发它们的科学家和进行检测的医疗人员--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。
