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Diagnosing malaria

Visit us (http://www.khanacademy.org/science/healthcare-and-medicine) for health and medicine content or (http://www.khanacademy.org/test-prep/mcat) for MCAT related content. These videos do not provide medical advice and are for informational purposes only. The videos are not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of a qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read or seen in any Khan Academy video. Created by Vishal Punwani.

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Video transcript

- How is malaria diagnosed? Well we can think about it basically as a three-step process. So remember that malaria is a disease caused by a parasite that's usually transmitted to humans through bites from infected mosquitoes. So if we want to know if someone has malaria we might start by asking them if they've been bitten. Or if they've been to anywhere that infected mosquitoes are known to hang around like in certain tropical or subtropical countries. We'd also double check to see if they were having any malaria symptoms like a flu-like illness or alternating chills and fevers. That's sort of typical of the malaria illness. So after we have this little conversation with the person, right that's step one in our three-step process, we would then move on to step two which is a physical exam. So remember that malaria has two phases. A liver phase where a whole bunch of sporozoites go in and infect the liver cells and then reproduce in the thousands and thousands of merozoites and then there's a red blood cell phase where initially those same merozoites they burst out of your liver cells and they get into your bloodstream where they infect your red blood cells. So in the physical exam well we kind of look for any clues on the outside of your body that might be able to tell us if these things are happening on the inside of your body. So we know something might be going on in the liver right? So we actually feel for the liver to see if it's enlarged because all of the inflammation that would be happening if the liver cells were bursting or if they were infected, that would make the liver enlarge a bit. The other physical things we look for on a person mostly have to do with red blood cells. So once the red blood cells start to get infected or once they start to get damaged, right because of all these merozoites tha are infecting them these damaged red blood cells start to collect in the spleen which lives all the way over here beside the stomach and the spleen is responsible for screening our blood and sort of pulling out and recycling any old or damaged red blood cells. So all of these damaged red blood cells are all of a sudden going to start filtering into the spleen and that will cause some congestion in the spleen and there's also some inflammation happening in here too now so the spleen starts to enlarge, starts to get bigger and in some cases it can enlarge really, really massively, so we try to feel for an enlarged spleen and remember red blood cells are bursting, right? And having lots and lots of nice healthy red blood cells is part of what gives us humans our nice warm coloring, right? To our skin. So if we're losing lots of red blood cells we would start to go pretty pale. So we look for pallor which just means abnormal paleness that happens when you don't have enough red blood cells circulating around. And this pallor is easiest to see in the hands and in the face. And then finally we might look for jaundice which will happen when bilirubin from inside the red blood cells get out and deposit under our skin. Good, so that's step two. That's our physical exam. Now on to step three. This is the most specific, the most definitive way of diagnosing malaria and it is a couple of lab tests. So there's a few different tests we can do to diagnose malaria, but I'll just describe the two most common ways. So one way is by a blood smear. So we take some blood from the person and we stick it on a microscope slide. You can see my next microscope slide here with blood on it. And then we look at it under a microscope to try to sort of directly visually pick out any malaria parasites, right. Just using our own two eyes. So you might've heard of a test called a thick an thin film. And that's actually what this is here. You can see that there's one sort of puddle of blood that's really thin, and the other puddle is a bit thicker, right. There's a bit more blood here. And anytime we look at blood under a microscope we just call it a blood film. So why do we need both the thick and the thin films? Well in the thick film we can zoom in a bit here. This is our thick film if we were to look at it through a microscope. This gives us a really broad view of the person's blood. So there's a good amount of blood here that we can see all at once within our microscope's field of view. So we're pretty quickly able to tell if it looks like there might be any parasites hanging around in there and indeed in this thick film we can see that maybe that's a little plasmodium there and maybe there's something going on over there and maybe over there. Again the main thing with this thick film is that we can look at lots at once to make sure we're getting a good representative sample of a person's blood. But we don't get too much detail in the thick film. And in fact remember that there's a couple different types of plasmodium. There's falciparum, there's vivax, there's ovale, but we can't really differentiate the amount on thick film. We need our thin film for that. So let's move over to our thin film. And you can immediately see that it's a lot more detailed right. Because it's thin, right. It's basically just a single layer of blood cells. They're not sort of all jumbled all over each other like in the thick film. So we can see more detail. And we can already see that there are some trophozoites in these red blood cells. It's kind of weird but this used to be the merozoite that infected this red blood cell initially. And now it has turned into a trophozoite which is what goes on to multiply into tons more merozoites. It reverts back to being called a merozoite one it starts to reproduce. And then here -- actually here is a red cell where that has already happened, right. This red cell is packed with merozoites. So we can definitely see that this person has a malaria parasite infection. Just by looking at the blood films. And we can actually also pick out this falciparum subtype of plasmodium on this thin film and right here, here's a vivax subtype. So on the thin film we can tell the difference. Alright one last test we'll talk about. So this one is called a rapid detection test, or an RDT. And this will give us our results in only about 15 minutes and you don't really need any training to do it. Whereas our thick and thin films, although theoretically they could be done really quickly you need -- well first of all you need a microscope and second you need someone with a really skilled eye to actually look at the blood films and these might not always be available. So RDTs, how do they work? Well essentially you take a drop of blood from usually a finger prick and then you actually collect the drop of blood with a special dipstick and this dipstick is really interesting. It kind of works like the pregnancy tests that can test your urine to see if you're pregnant. Except obviously this is testing for malaria and hopefully using your blood and not your urine. So here's the dipstick and on it there's all of these antibodies stuck all over its surface, right. And so these antibodies essentially look for two different things in the blood. So let me set you up here. So when red blood cells get infected with malaria parasites our red cells start to produce enzymes that end up being displayed. They get stuck onto the outside of our red cell membranes. And so some of the antibodies on the dipstick they'll be looking to grab onto any of these enzymes that they might be able to find in the blood sample right. Because that could mean that there's a plasmodium infection. One issue with that is that some of the enzumes only get produced in plasmodium falciparum infections and not in infections by other types of plasmodium. And that's still usually okay because remember falciparum causes the vast majority of infections. But in any case the dipstick also looks for something else so each subtype of plasmodium produces a slightly different version of an enzyme that they all have, called plasmodium lactate dehydroginase. Or PLDH. So this is an enzyme that helps the plasmodium make energy to do all of its dirty work. And so our dipstick it actually has antibodies on it that can bind to each of the different PLDHs that the different subtypes of plasmodium would make. So based on the kind of PLDH that our dipstick antibodies bind to, that's how we know what type of malaria parasite we're dealing with. And that's important. Because some subtypes need their own special kind of treatment for us to completely remove them from our system.