This video, we're going to talk about the plasmodium life cycle and malaria. Now, malaria is actually one of the deadliest diseases in the world, killing about 600,000 people every year. And it's a common misconception that malaria is caused directly by mosquitoes, but that's not actually the case. Instead, malaria is caused by a protist called Plasmodium, which enters and exits humans via mosquito bites. And so mosquitoes get all the blame, but really, it's the plasmodium's fault.
Now, the plasmodium lifecycle actually requires multiple hosts in order to fully complete its lifecycle. It requires a mosquito host and a human host. Also, the plasmodium lifecycle contains both sexual and asexual stages, and we'll be able to see this in this diagram of the plasmodium lifecycle. So let's go ahead and enlarge this diagram so we can see it more clearly and notice that we've broken up this lifecycle into 7 steps that we have numbered throughout this diagram. So let's go ahead and wipe this diagram clean so we can approach this one step at a time.
Notice that the arrow over here on the left in orange represents events that occur inside of the mosquito host, whereas the arrow over here on the right in blue represents events that occur inside of the human host. And this is very important to pay attention to moving forward. Now let's go ahead and kick off this life cycle process with an infected mosquito biting a human. And, of course, the mosquito is going to be infected with the Plasmodium protist, more specifically, an infectious form of the Plasmodium protist called sporozoites, which are actually haploid in nature. And so we can consider this mosquito bite step number 1 of the life cycle.
Now, of course, upon biting the human, the sporozoites from the infected mosquito will be injected into the bloodstream of the human host, and the sporozoites will travel through the bloodstream to the human liver and infect the liver cells. Step number 2 is that the liver cells get infected by these sporozoites. Then, these sporozoites will develop into yet another form of the plasmodium protist called merozoites, and these merozoites will reproduce asexually via mitosis until they cause these liver cells to lyse, releasing a whole bunch of merozoites into the blood. Now in step number 3, these merozoites are going to infect red blood cells and reproduce asexually via mitosis inside of the red blood cells until they cause these red blood cells to lyse and burst open, destroying the red blood cells and releasing a whole bunch more merozoites that can continually go on to infect and destroy more and more red blood cells. And really, it's this step number 3, the infection and destruction of the red blood cells that causes the signs and symptoms associated with malaria, such as fever and chills.
Now in step number 4, some of these merozoites are going to develop into gametocytes, which are precursors to gametes. However, these gametocytes will not be able to develop into gametes inside of the human host. These gametocytes require very specific conditions in order to develop into gametes, and those conditions are only found inside of the mosquito host. And so notice that we're transitioning from the blue arrow over to the yellow arrow, which means that we're now transitioning over to the mosquito host. So let's say that an uninfected mosquito that does not have this plasmodium protist in it comes and bites this infected human.
Well, this mosquito bite is going to be step number 5, and that's going to allow the gametocytes from the human to be transferred over into the mosquito host. Now once inside the mosquito host, these gametocytes will develop into the gametes, the male form and female form, forming sperm and egg. And, of course, these gametes can fuse together in the process of fertilization, which is step number 6, to create a zygote. And the zygote is going to be diploid in nature, so we can put 2 n here in this blank. Then the zygote will undergo meiosis followed by several rounds of mitosis to produce a whole bunch of sporozoites that are haploid in nature.
So we can put an n here, and these sporozoites will travel to the salivary glands of the mosquito so that it can actually inject the sporozoites into the next human that it feeds on. And so this here completes the full life cycle of the Plasmodium protist, and moving forward, we'll be able to apply these concepts and problems and look at other protist life cycles as well. So I'll see you on our next video.