Plasmodium Falciparum Life Cycle

by Vincent Racaniello, PhD

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    00:00 Let’s take a look at the lifecycle of Plasmodium falciparum, both in the mosquito and in the human host. There are slight differences between falciparum and the other species, but this will suffice to illustrate the general pattern. We start at the top of the slide with the mosquito injecting parasites, we are going to continue through the liver stage, the blood stages and eventually we’re going to get back into the mosquito. So this is a cycle that is maintained among people by the mosquito vector. So let's look at step one, the mosquito, again it's a female mosquito, is biting someone and delivering the form of the parasite called a sporozoite. Sporozoites come out of the salivary gland of the mosquito and the mosquito of course is taking a blood meal, so the mosquito inserts its proboscis into the skin, it actually injects some saliva because that saliva contains a variety of compounds to make it easier for the mosquito to draw a blood meal, like anticoagulants and other things as well. And of course if the mosquitoe is infected, it will deliver sporozoites as well. So the simple fact that the mosquito has to take a blood meal, injects those sporozoites and of course the mosquito will withdraw blood from that host. Those sporozoites are then entering into the circulatory system of a human. Within 30 minutes, those sporozoites go to the liver. This is going to be their main stop on their trip through the human body, and they become a form called cryptozoites. Now many parasites go through multiple stages in their life cycles with various names, sporozoites, what’s in the mosquito, cryptozoite is what the sporozoite becomes in the liver. The parasite replicates in the liver and it does so inside an infected cell and that cell eventually produces many, many merezoites, the cell ruptures within 18 to 14 days after the initial mosquito bite, and those new merozoites are released into the bloodstream. In the blood, the merozoites then infect its second target which is the red blood cell. They enter the red blood cell in which they multiply. Now here we’re showing you several of the stages that occur within the red blood cell, starting from the top, the free moving red blood cell that’s infected with what we call ring forms, you can see those two on the upper left, and then below it are the different forms of the infective stages within the red blood cell. If you do smears of infected individuals, you’ll see all these forms in the blood. And in the blood the merozoites multiply and at some point the blood cell ruptures and releases more merozoites into the bloodstream. This kind of multiplication that we've been talking about, both in the red blood cells and in the liver, is asexual. It’s simply binary fission. But at some point in the reproduction, the sexual stages are made, and this is an organism that can reproduce in both ways, sexually and asexually, so at some point during the replication both male and female gametocytes, that's the name for the sexual stage of the organism, are made and now these will be picked up by a new mosquito, if this person who is now full of malaria parasites is bitten and of course if you're in an area endemic for malaria, it's likely that you will bitten thousands of times a day, so mosquitoes will deliver malaria parasites and they will pick up new ones from infected people. Now when a mosquito takes a blood meal, the blood goes to the gut of the mosquito of course, because that's where it is digested. And so go the male and female gametocytes, they will eventually mate and produce the asexual stages and so from the gut the two gametocytes will mate, they will migrate back to the salivary gland, of course that is where they need to be to be delivered to the next victim, so sexual mating in the mosquito and the production of sporozoites, which are then going to be delivered to the next host.

    About the Lecture

    The lecture Plasmodium Falciparum Life Cycle by Vincent Racaniello, PhD is from the course Parasites.

    Included Quiz Questions

    1. Sporozoite
    2. Gamaeozoite
    3. Schizont
    4. Early Trophozoite
    5. Merozoite
    1. Merozoite
    2. Gamaeozoite
    3. Sporozoite
    4. Schizont
    5. Early Trophozoite
    1. Male and female gametocytes
    2. Male gametocytes
    3. Schizont
    4. Female gametocytes
    5. Merozoite

    Author of lecture Plasmodium Falciparum Life Cycle

     Vincent Racaniello, PhD

    Vincent Racaniello, PhD

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    well done
    By Helen D. on 30. September 2018 for Plasmodium Falciparum Life Cycle

    great presentation and eloquence. the lectures are well done and easy to understand. great information, and would highly recommend it.