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Video transcript

- [Voiceover] What is malaria? And, importantly, why do I have this mosquito drawn here? That seems a little bit weird. Well, the mosquito here is actually pretty important. Malaria is a disease, an infectious and often fatal disease that is transmitted to humans and other animals as well, not just humans, but it's transmitted most often by us being bitten by an infected mosquito. And, interestingly, malaria is primarily a disease of the liver and of the red blood cells. And as you'll sort of see in a few minutes here, this kind of explains some of the symptoms that we see in malaria, and we'll talk about those a little bit later on. But, first, let me zoom in here, and let's talk about what happens in a mosquito bite. So, here's our skin, right? And we'll say that these are blood vessels under the skin. And here's our blood. And out here is our friendly, well, not so friendly in this case, but our mosquito. And what is she doing here? Like, why are mosquitoes always biting us? Well, it's because they need to feed on blood in order to survive, right? They're like little flying vampires, which, incidentally, is my personal worst nightmare. So, that's what she's doing around here. She's trying to get at our blood by biting us. Real nice. So, to do that, she will poke her little proboscis, that's what this pointy mouth thing is called, the proboscis, through our skin, to access all of our blood vessels underneath. And, from there, she'll start to suck up some blood, right, and she'll start to fill up her little thieving tummy. And then, she'll take off, all satisfied, right? She's happy and she goes off. And that's not usually a problem for us. I mean, I'm not advocating for mosquitoes here. People get bitten by mosquitoes all the time, and they're fine. But some mosquitoes, particularly ones that live in certain more tropical parts of the world, right, closer to the equator, like some African countries and some Asian countries, and some, some Latin American countries, some mosquitoes, the majority of which are in these areas, carry a parasite called plasmodium. And there is a couple of different types of plasmodium, but for now, we'll focus on Plasmodium falciparum, falciparum, because this type causes the highest number of deaths in humans. All right. So, now, let's add in some parasites to our mosquito here and see what happens when someone gets bitten by an infected mosquito. And, actually, let me point out that I keep saying "she" when I talk about our mosquito here, and that's because the plasmodium parasite is usually transmitted by a female Anopheles mosquito. Anopheles is just the genus. And that's because females feed on blood while the male mosquitoes feed on other things, like nectar from flowers and plants and such. So, how does she do it? Well, once she's happily sort of drinking our blood, some of the parasites from within her saliva, they'll sort of swim over from inside her mouth to our bloodstream. So, that's kind of step one of the infection. And what happens after that is that the parasites, which are actually called sporozoites at this stage, they have their own special name, sporozoites, and there's usually a whole bunch of them, they swim through our bloodstream until they get to our liver. And then, they say to themselves, "Hey, this looks like a really fun place to hang out. "Let's stay here for a while." So, they do. They actually infect our liver cells, and they hang out in the liver for a couple of weeks, usually about two weeks. And when they're in our liver cells, they're not just passively hanging out. They're actually reproducing. So, they're asexually reproducing and they're creating thousands of little parasite babies, little offspring. And so, they reproduce and they reproduce and they reproduce for a couple of weeks until they build up this massive army of merozoites. That's what they're called at this stage, merozoites. And when they're good and ready, they burst out of our liver cells, which obviously kills the liver cell, unfortunately, and they enter back into the bloodstream. And so, this form of plasmodium, merozoites, they're going to go on and infect our red blood cells. So, they'll find red blood cells in our bloodstream, not really too hard to do, and from there, they'll get inside them. Red cells are their new home. And, you know, from here, things get even more interesting. So, some of the merozoites, they do exactly what they did in the liver cells. They asexually reproduce. They create tons and tons and tons of new merozoites, which burst out of the red blood cells and go on to infect more red blood cells. But another group of merozoites, once they infect a red blood cell, they kind of shape-shift. They do this really weird thing where they change form into what are called immature gametocytes, and some will be male, and some will be female. And this will all make sense in a minute here, so you'll just have to bear with me for a second, and you'll see what these gametocytes do. So, what happens now? Well, when we get bitten by yet another mosquito, right, these darn flying vampires, whether they're infected or not, there's a really good chance that while they're siphoning up our blood, they're going to suck up some of the red blood cells that contain these male and female gametocytes. And here's the really wild thing. The gametocytes need to actually be inside a mosquito's gut to mature. It's incredible. So, the male and the female gametocytes, because of the, I guess, the sort of environment within a mosquito's gut, they fuse together to create a zygote. And then this plasmodium zygote goes on to develop into a new sporozoite. Remember, the initial infective form? And then, the sporozoite goes on and swims back up to the mosquito's salivary glands. So, now, they're ready to be injected back into another human host. It's incredible. So, this is sort of a really bizarre example of the circle of life, probably not the kind of example you had in mind when you were watching the Lion King, I'd imagine. So, these plasmodium parasites rely on both mosquitoes and some warm-blooded animal to reproduce. Unfortunately, this group of warm-blooded animals includes us humans. So, before we wrap up, I just want to briefly talk about the symptoms that you'd experience if you had a malaria infection. So, generally, it takes about two weeks after being bitten by an infected mosquito before we start seeing any symptoms. So, why is that? Well, remember that the plasmodium sporozoites travel to the liver and hang out for a couple of weeks. So, them hanging out is exactly what that couple of week asymptomatic period is. But when they sort of burst out of our liver cells and then later on start to burst out of our infected red blood cells, that's when we start to see the classic symptoms of malaria, as we start to lose red blood cells and as the immune system starts to take notice. So, when the immune system gets involved, it kicks off a flu-like syndrome. So, just picture what you felt like when you last had the flu. It's really similar to that, but quite a bit more dangerous. So, things like really high fever and headache and, you know, muscle pain, and just generally feeling really unwell. And there's actually a classic symptom associated with malaria called paroxysm, temperature paroxysm, where the person will sort of cycle between sudden coldness and shivering and fever and sweating. And these paroxysmal symptoms, they kind of come on and off about every 36 to 48 hours, every couple of days. And that's because these symptoms are actually directly related to, right, they're representative of these waves of merozoites bursting out of the liver and the infected red blood cells at these staggered sort of cyclical times, once they build up enough to launch a new wave, essentially. And remember how I said that red blood cells are getting destroyed. Well, red blood cells, inside them, they have these proteins called bilirubin proteins. And when they leak out into our bloodstream, they tend to deposit under our skin. And just them being there gives our skin a bit of a yellowish tinge. So this is known as hemolytic jaundice, jaundice referring to the yellowing of the skin, and hemolytic means the bursting of red blood cells, which is why it's happening. So, the last thing I'll mention, we classify an illness with malaria into two broad groups. So, uncomplicated and severe. So, uncomplicated malaria would be an infection where a person has just these symptoms that I've described, right? Flu-like symptoms with this paroxysm and maybe some jaundice. And this type is pretty easily treated with medications. There's anti-malarial drugs that can kill off the plasmodium parasites. And the person can usually get back to being a hundred percent better. But there's also a severe malaria, which is when the person will also develop some serious organ problems, like maybe some lung problem, so they can't breathe properly, or some circulatory problems like super-low blood pressure, or severe anemia because of all these blood cells that are rupturing, or they might develop some brain problems, which might make the person really weak or might give them a really decreased level of consciousness. So, if a person has severe malaria, they need to be taken to a hospital right away, because in addition to the sort of standard anti-malarial drugs, they will likely need intensive care and constant monitoring to maximize their chances of survival.