Trypanosoma Brucei

by Vincent Racaniello, PhD

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    00:00 vector, the tsetse fly.

    00:01 Let's take a look at the pathogenesis of Trypanosoma Brucei. Here is an overview. Again these are spread by tsetse flies, they inoculate the parasites, a lesion forms at the site of inoculation, they become blood parasites in the host and then the fly takes up parasites and repeats the cycle again, and then there are some consequences of infection that we will talk about. So the infected tsetse fly is taking a blood meal of course, that's why it's biting you. It takes a blood meal, but in so doing, it first injects saliva. This is a common theme among the mosquitoes and sand flies and tsetse fly vectors that spread these diseases. To take a blood meal, you first inject saliva in order to give chemicals that will for example prevent clotting of blood and in so injecting that saliva, there go the parasites with it. You develop a primary lesion at the bite site, that second circle there, which is highlighted, that is a lesion on the surface of your skin, we call that a chancre. The bloodstream then becomes invaded by trypomastigotes, those are those flagellated forms of which a photo I showed you earlier, which I think are quite beautiful, unfortunately not very good for you. They invade the bloodstream and of course once they are in the blood, they can take a trip to wherever they please. You develop a systemic illness as a consequence of the global distribution of the parasite within you with fever and lymphadenopathy, that is swollen lymph nodes. After months in the case of the rhodesiense, or years in the case of the gambiense, these parasites may invade the central nervous system. So you see here at the bottom of the right hand part of this slide you have a brain being invaded by the parasites. An early sign that this is happening is called Winterbottom's sign. It's a swelling at the back of the head, as you can see in this gentleman. If you see this on someone who you know is infected, that is a bad sign. It means the parasites are likely going into the central nervous system and there you cannot have good consequences. The right-hand circle at the bottom there, shows you a form of pathology caused by infection called perivascular cuffing.

    02:37 When parasites are present in the blood, immune cells go around the blood vessels and in a cross-section such as this. You can see the dots are all around the blood vessel and that's called perivascular cuffing. That can be used to diagnose infection. Now you may be understanding already at this point that this infection has gone on for months or years and apparently it's not being cleared. Well if you thought that, you'd be absolutely right, because during all these months and years of chronic infection, you have waves of parasitemia. So what happens is, the parasites get in your blood, we make an immune response that clears the infection, but a few are left, a few parasites are left that are not stopped by the antibody. They have changed their code and so those grow and you have another wave of parasite. You then make antibodies against those and of course all this time months are going by, your antibodies clear most of those, there are a few left, who have changed their code again and this goes on and on and on. This is a hallmark of Trypanosoma brucei, antigenic variation. We can't get rid of this infection naturally, quite a brilliant strategy. So here is an example of this antigenic variation. There is on the X axis time and weeks, and these are blood samples taken from an individual at different weeks after infection and we are measuring the number of Trypanosomes in the blood on the Y-axis. You can see there's a peak and a trough, and another peak and a trough, etc. etc. This happens with real regularity. As the parasites grow, they are eliminated by the immune response, they change, they grow again and so on and so on. This is the real problem with trying to clear this infection. Now in the end, if you are infected, the fly, the tsetse fly can bite you and ingest blood and of course take parasites up in the process and start the cycle all over again.

    About the Lecture

    The lecture Trypanosoma Brucei by Vincent Racaniello, PhD is from the course Parasites.

    Included Quiz Questions

    1. skin
    2. stomach
    3. eyes
    4. liver
    5. spleen
    1. Trypomastigote
    2. Male gametocytes
    3. Amastigote
    4. Schizont
    5. Merozoite
    1. Swelling at the back of the head
    2. Splenomegaly
    3. Rhinitis
    4. Blackening of skin
    5. Excessive lacrimation
    1. antigenic variation.
    2. toxin production
    3. polysaccharide capsule
    4. IgA protease
    5. Haemagglutinase

    Author of lecture Trypanosoma Brucei

     Vincent Racaniello, PhD

    Vincent Racaniello, PhD

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