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  • [♪ INTRO]

  • This episode was filmed on April 21st, 2020.

  • If we have any updates on testing, we will link to them in the description.

  • It's always been helpful to be able to test for specific ailments.

  • But during a pandemic, testing becomes essential,

  • because it's much harder to fight a disease when you don't know who has it.

  • And detecting pathogens isn't as easy as checking off a list of symptoms.

  • For example, as we noted a few weeks ago,

  • the new coronavirus behind COVID-19 may have distinctive symptoms,

  • or, it may look a lot like seasonal allergies or the flu or it may look like nothing at all.

  • So to be sure of infections, you have to run some kind of test.

  • Until recently, that could take days;

  • in part because the test itself takes several hours to run,

  • but also because it has required getting samples to specialized labs with expensive equipment.

  • But the new wave of COVID tests can be run by hospitals and doctors on-site,

  • and many turn around results in an hour or less.

  • And that's because they take advantage of some really cool molecular biology.

  • The tried-and-true, and somewhat slow, method for detecting coronavirus

  • is something called RT-PCR.

  • If you got a COVID test any time before, like, right now, so late April,

  • it was almost definitely tested this way.

  • The short version is that RT-PCR uses molecular tools

  • to spot the viruses' genetic material lurking in your bodily fluids.

  • The RT stands for Reverse Transcriptase,

  • an enzyme that lets us turn the virus' RNA genes into DNA.

  • And then PCR stands for Polymerase Chain Reaction,

  • a technique that makes /billions/ of copies of that DNA so it's easier to see.

  • Because, you know, DNA molecules are pretty small.

  • This whole process takes a few hours because the PCR bit

  • requires lots of temperature cycles that take several minutes each.

  • So you could detect the virus a whole lot faster

  • if you could somehow speed up this DNA copying.

  • And it turns out you can, if you use isothermal amplification instead.

  • You see, the reason PCR involves a lot of heating and cooling

  • is that it uses heat to separate DNA into individual strands.

  • Isothermal meanssame temperature,” so isothermal amplification

  • uses DNA-copying enzymes that can unwind

  • and separate DNA strands all by themselves, no heat cycling required.

  • So the most common variety of this method, called LAMP,

  • also adds several special primers, which stick to each other.

  • These warp the DNA into weird dumbbell shapes,

  • and that creates open starting points for the enzymes that actually do the copying to latch onto.

  • Tests relying on this kind of amplification weren't rolled out as quickly as the RT-PCR tests,

  • possibly because it can be challenging to design those special primers.

  • These are the basics.

  • It's actually a little bit more complicated than this,

  • but the benefit is that the machines only need to hold at one temperature,

  • so they can be much smaller, much cheaper, and much more portable.

  • The copies of the DNA are made much faster, too.

  • So much faster that one company's US FDA-approved test can deliver results within 15 minutes!

  • Though, that's with their not-so-cheap, all-in-one machine and one-time-use cartridges,

  • which not all doctors or hospitals have on hand.

  • And each of these machines can only run one test at a time.

  • So you need lots of them if you want to run a lot of tests in one day.

  • Other groups developing COVID-19 tests say

  • their isothermal amplification can take 20 to 30 minutes.

  • They then spruce up the detection side of things, too,

  • by using a super-precise CRISPR system.

  • Usually, when we're talking about CRISPR,

  • we're talking about editing DNA using CRISPR/Cas-9.

  • The Cas9 is an enzyme designed to recognize specific genetic sequences,

  • and when it does, it snips them out, like laser-guided scissors.

  • The enzymes in CRISPR-based virus tests, on the other hand,

  • are Cas-12 or Cas-13, which are more like paper shredders.

  • When they find genetic material they recognize,

  • they cut that sequence as well as any other DNA or RNA around it.

  • The tests also include reporter molecules that do things

  • like glow or change color when this shredding happens.

  • So basically, if you see something change,

  • then the enzyme has found the viral genes, and the test is positive.

  • These can take less than an hour to run, from swab to result,

  • and they don't need a lot of fancy equipment,

  • so they can be performed on-site at a doctor's office or in a hospital.

  • Initial results from one suggest that they're about as accurate as standard PCR tests.

  • They might also be super-precise, able to detect even a single letter change in a virus' genome.

  • But you won't see these CRISPR tests in your doctor's office quite yet.

  • They're taking a little while to develop and test - as with any newish technology,

  • researchers want to be extra sure they are reliable and accurate before rolling them out.

  • Meanwhile, some companies are working on even faster tests that are also easier to use.

  • These tests don't search for viral genes.

  • They're called immunoassays because they detect pathogens using antibodies,

  • Y-shaped molecules created by our immune system in response to infections.

  • So immunoassays don't detect antibodies,

  • they use antibodies that are found somewhere else to detect the presence of the virus.

  • The immune system is complicated, but basically,

  • antibodies work by sticking to specific things.

  • And immunoassays use this stickiness to their advantage.

  • Essentially, they take a patient's sample and incubate it

  • with lab-grown antibodies specifically tailored to target the pathogen.

  • Additional ingredients, like enzymes that'll change color if the antibodies hit their mark,

  • then let the doctor see if the sample is positive.

  • Antibodies can be grown in lab animals that have been exposed to the virus or parts of it,

  • or even from the blood cells of people who have recovered.

  • Or, the gene for a desired antibody may be inserted

  • into the genome of a bacterium or yeast to coax it to mass-produce them.

  • The trick is finding the right antibody,

  • one that reliably sticks to what you want, and not to anything else.

  • That's why immunoassays take longer to develop than RNA- or DNA-finding tests.

  • They can also be a bit less accurate.

  • But once they're ready, they're generally much easier to use and lightning quick.

  • They can even be put into dipsticks, like a home pregnancy test,

  • that require no fancy equipment at all.

  • So, one could imagine something similar coming onto the market

  • that uses a drop of blood from a finger prick to spot the SARS-CoV-2 virus.

  • And at least one antibody has been created for the new coronavirus,

  • so this kind of test is probably on the horizon.

  • Now, all of these tests are useful, even essential, but they have a blindspot.

  • They can only detect if a person has the virus inside them right now,

  • not if they've been exposed and fought it off.

  • Luckily, the antibodies a person generates to fend off a pathogen

  • tend to stick around in their body for at least a little while afterwards,

  • forming a kind of immune memory and helping ward off future infections.

  • And researchers have also been designing tests to look for those antibodies in our bodies.

  • So, essentially, this is the reverse of the test we just talked about.

  • Instead of using antibodies to detect the virus,

  • these tests generally use bits of the virus to detect antibodies.

  • For one technique, called an ELISA,

  • you add a patient's serum to a special plate coated in viral proteins.

  • You also add a protein or a compound that produces some kind of signal

  • if antibodies in the serum bind to the bits of virus.

  • So, if you see a signal, you know that person has had COVID.

  • Because it takes a little bit for your body to make these kinds of antibodies,

  • this kind of test isn't really useful for figuring out if someone has been infected.

  • It might tell you they have the antibodies,

  • in which case they probably have been infected but might not be currently,

  • or they might be infected and not have the antibodies yet.

  • But these tests can be really important for helping health authorities

  • track chains of infection and understand how the virus is spreading.

  • So soon, hopefully, doctors will not only be able to quickly determine

  • whether a patient has COVID, they'll be able to see if they had it in the past.

  • These data will help health professionals track the pandemic

  • and determine the most effective actions to take.

  • So all these new tests aren't just improving on tried-and-true methods,

  • they're helping us fight diseases faster and more efficiently.

  • Thanks for watching this episode of SciShow News!

  • To find more of our coverage of the COVID-19 pandemic,

  • you can check out the playlist in the description.

  • Before I go, I'd like to give a special thank you to everyone who watches and supports SciShow,

  • especially our patrons on Patreon.

  • We are not exaggerating when we say we couldn't make episodes like this without our patrons.

  • So thank you to all of you who are members of that wonderful community.

  • And if you want to learn more about joining that awesome group of people,

  • you can head over to Patreon.com/SciShow.

  • [♪ OUTRO]

[♪ INTRO]

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