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Video transcript

- [Voiceover] When we're trying to diagnose syphilis, which I'll abbreviate like this, because it's shaped like a spiral, that's why it's called a spirochete, but other times we'll call it a treponem. So when we're trying to diagnose syphilis, one of the downsides is that we can't diagnose the specific stage. So those signs and symptoms are used to determine what stage of syphilis a person has. Now there are two types of diagnostic tests to determine whether a person has syphilis. The first set are referred to as non-treponemal tests, and remember that treponemal just refers to the genus name of the syphilis bacterium, treponema. And in contrast, there are also treponemal tests that we can use to diagnose syphilis in a person. And the main difference is that non-treponemal tests are mainly used to screen patients, so they're for screening, whereas treponemal tests are for confirming a diagnosis in a patient that's already been screened. Which means that we usually do our non-treponemal tests first, and then we do treponemal test afterward. Now as the name suggests, non-treponemal tests don't use proteins from the syphilis bacterium. Whereas treponemal tests will use proteins that were grown and taken from the syphilis bacterium. Now the first non-treponemal test we'll talk about is kind of a mouthful, it's referred to as the venereal disease research laboratory test. The venereal disease research laboratory test. And the way it works is that you get a sample of the patient's blood, so I'll label here, this is the patient's blood, and you add that to this well right here. This well will have, strangely enough, a sample of ox heart extract. So this has ox heart extract, which is kinda weird. But the reason why we use this is because ox hearts tend to have a protein that I'm drawing right here, and I'll draw this protein up here again. They have this protein that antibodies from our blood sample will mistake as syphilis treponem proteins. Which means that if this patient has been infected with syphilis and they have this antibody right here, that is supposed to bind syphilis proteins, we will see when they're combined, so I'll draw this guy over here. So when we combine these two, we'll see the anti-syphilis antibodies binding to this protein that's found in the ox heart extract. And after we add a fluorescent tag or a dye that allows this reaction to light up, we can actually visualize it under a microscope. Therefore, indicating a positive test. Now moving on, the next non-treponemal test we can do is referred to as a rapid plasma reagin test, a rapid plasma reagin test, or RPR. Which, as you can see here, is exactly the same as the VDRL test, the only two differences is that we add these carbon particles to our well. So these carbon particles are present here. So I'll write in our legend down here that these are carbon particles, that will help us if there's a reaction that is present here, to see the binding of the antibody with the protein, not with a microscope, but with our eyes. So as you might imagine, the rapid plasma reagin test tends to be faster than the VDRL test. And overall both of these tests, these non-treponemal tests, tend to have high sensitivity, meaning they're unlikely to have false negatives. But they have low specificity, which means that it's possible that a positive test may be wrong or false. As you might guess from using the ox heart extract rather than the actual protein from treponems. There are several viruses, drugs, even rheumatic heart disease, or even lupus, can cause a false positive. So that's why once we screen for syphilis with these tests, we need to confirm our diagnosis. And we do that by directly using the treponem protein. The first test I'll mention is what's called a treponema pallidum, or just the name for the syphilis bacterium, the treponema pallidum hemagglutination assay. Or we can abbreviate this mouthful as a TPHA test, a TPHA test. And the setup for this test is very similar to what we saw earlier with the non-treponemal tests as you can see here. But instead this is a sample of the syphilis antigen, which I'll draw here not as a darker green, but as the exact green I've been coding syphilis to be. And I think you know what happens from here. You'll get the antibody binding onto the syphilis antigen that we've grown in a laboratory, and this actually happens to such a huge extent, that you'll actually see the blood to start clumping. It's cause we'll have a lot of the antibodies present and they're just going to feast on the syphilis protein, just feast all over it. So this clumping phenomenon, so I'll write here, clumping, is also known as agglutination. Which is where this test gets its name. You use the treponema pallidum antigen to cause your blood to clump, which would confirm the diagnosis. The last of the treponemal tests I'll mention is what's referred to as a fluorescent treponemal antibody, which I'll abbreviate as Ab, but fluorescent treponemal antibody absorption test. Which in some places you might see abbreviated as FTA-AbS. So an FTA-AbS test. Now this is a similar setup as the hemagglutination assay test we saw above. As you can see here, and I'll take this minute to label the antibodies I've been talking about, are that protein in the blood there. Now the main difference between this test and the hemagglutination assay, is that you also add a drop of this fluorescent tag, similar to what we were doing earlier with the non-treponemal studies in both cases when we had this fluorescent tag. And all this represents, is a dye that will bind the antibody if it ends up grabbing onto the syphilis protein here, or the syphilis antigen. So what you should see here, is the antibody binding onto the syphilis antigen, maybe you'll even get some clumping going on as well. But what cinches the diagnosis here, is that this will light up, because the antibodies will be binding onto this fluorescent dye as well. Therefore, confirming the diagnosis. As you might have noticed, because these two tests are very similar, the TPHA test is considered to be easier because we don't have to take that extra step to add the fluorescent dye. But it's not as sensitive, it's not as sensitive as the absorption study here. Which should be okay, because we want a high-sensitivity test when we're screening, and when we're confirming that we have syphilis, we want to use a test with high specificity. So we have a low likelihood of false positives. Which is the case here with the treponemal tests. Now the last test I'll mention is the one that I think has the coolest name, this is dark field microscopy. So dark field microscopy uses a special type of microscope to look at a sample taken from a patient. So let's say this is a sample I have on this Q-tip here, and I've performed a cervical swab on a female patient that we're suspecting is infected with syphilis, and we wanna take a look at this under a dark field microscope. Well, if this patient does in fact have syphilis, you'll actually see spirochetes under this microscope. So as you can see here, these squiggly things are the syphilis treponemal spirochetes that are present in this sample, how cool is that? So if you see these guys under the dark field microscope that's a very high-specificity test, which means you're less likely to have false positives, and instead confirm that this person is infected with syphilis. All right, so let's say that we've confirmed someone has been infected, how do we go about treating them? Well the mainstay of treatment for syphilis is the use of antibiotics. And for a person that has a more advanced stage of syphilis, such as secondary or tertiary syphilis, all they would need is just longer therapy. The one issue a patient may have when they're being treated for syphilis is what's referred to as a Jarisch-Herxheimer reaction. A Jarisch-Herxheimer reaction. And all that means is that when you kill the syphilis, so you've got dead treponemes in the bloodstream, these guys will release toxins. And that will trigger white blood cells to react to them. And they will in turn release cytokines, that can trigger things like a fever, muscle pain, headache, and even a fast heart rate, which we call tachycardia. So tachycardia, a fast heart rate. And as you can probably tell, all of these symptoms are pretty terrible, but over time as you clear the syphilis bacteria from your bloodstream, they'll go away. So all of these symptoms are just transient. Now finally, how do we prevent transmission of syphilis? And the answer here is just to decrease direct contact with an infected patient when having sex. And so we earlier talked about the three different types of sex, like vaginal sex, anal, and oral sex, that we can prevent transmission by using condoms. In the case of oral sex, we can additionally use dental dams to block transmission. And remember also that childbirth is a very important mechanism for the spread of syphilis from a mother to a newborn child. And the solution there is to screen for syphilis, and in an infected mother, just treat mom to make sure that she doesn't spread the disease to her newborn child.