Cutaneous Leishmaniasis

by Vincent Racaniello, PhD

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    00:00 So here is the lifecycle of leishmania tropica and we see it has a mosquito cycle and a cycle in people. Now remember this parasite can be acquired largely from other animals, the horse, dog, animal, the mouse in the upper right there, but it can also be passed from human to human. And again the phlebotomous sandflies pick up the parasites, deliver them to humans and then they are passed around to other animals as well. Now on the lower right part of this slide, you can see a hand with a lesion on it, this is cutaneous leishmaniasis.

    00:39 Wherever the sandfly bites, that's where the lesion occurs, if it's on your face, you're left with a scarring lesion. So first here is a sandfly picking up the amastigote form of the leishmania, which it can do from many different mammals. On the top right, non-human animals and human animals as well. It takes a blood meal, it pulls up the parasites into its gut of course and there it will undergo a number of transformations and make its way back to the salivary gland so that it can be delivered through the saliva, to another host. The sandfly acquires the amastigote form, that's shown on the lower right, that form goes to the gut tract, it then transforms into flagellated promastigotes. These are freely swimming forms of the parasite, they replicate in the gut tract, make their way to the salivary gland, which you can see in the middle circle there and that's how they get delivered to a new host. Of course if they remained in the gut tract, they wouldn't get delivered to a new host because the contents of the gut are not injected when a biting animal, a biting fly bites a new host. So then, once the parasites have developed and moved to the salivary gland when the sandfly bites a new host, they can be injected into another animal. And as I said, very important observation, in endemic areas, that means areas where there are lots and lots of leishmania infections of humans, it is possible that the sandfly could bite an infected human, pick up leishmania parasites and deliver it to another human or perhaps even another animal that it's biting. This has to be an area of very high density infections, because as you can imagine, if there are just a few human infections, it is not likely that a sandfly bite is going to pick up the parasite from them, more likely picking it up from animals, which are more heavily infected. Once the sand fly injects the parasite, the flagellated form, into the skin, it leads to tissue destruction and the formation of a lesion at the site of the bite, which you can see on the hand shown here. And this is in part due to the fact that the flagellated forms are taken up by macrophages, they replicate in the macrophage, the macrophage is destroyed, it releases a variety of chemicals that then destroy the surrounding tissues. So this can be a lesion of an inch or so in diameter. On the hands it's of no consequence, but of course it often happens on the face, you can be bitten there, these are typically not treated and you have a scar for the rest of your life, unfortunately.

    About the Lecture

    The lecture Cutaneous Leishmaniasis by Vincent Racaniello, PhD is from the course Parasites.

    Included Quiz Questions

    1. Amastigote
    2. Promastigote
    3. Protomastigote
    4. Schizont
    5. Macrophage mastigote
    1. GI tract
    2. Thorax
    3. Proboscis
    4. Salivary gland
    5. Palpi
    1. Release of chemicals from macrophages
    2. Sandfly saliva contains proteases
    3. Sandfly saliva has low pH
    4. Sandfly saliva contains anticoagulants
    5. Release of antihistamine from mast cells

    Author of lecture Cutaneous Leishmaniasis

     Vincent Racaniello, PhD

    Vincent Racaniello, PhD

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