Infections by Chlamydiae and Rickettsiae

by Richard Mitchell, MD, PhD

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    00:01 Well, let's move up the phylogenetic tree and talk about chlamydia.

    00:04 So this is an obligate intracellular organism.

    00:07 It has a DNA and it has an RNA and it has disulfide linked-cell wall, so some of the characteristics of it.

    00:15 It's pathology occurs because it uses up all the host ATP and will cause a lytic infection on that bases.

    00:23 Now, the lytic infection occurs when we have growing within the cell, as you can see on the right hand side, reticulate bodies.

    00:32 These reticulate bodies are slightly larger, they're proliferating, but they will mature into their elementary bodies that then can go out when the cell ruptures, and in fact, the next cells, so those are the infective particles.

    00:44 Diseases that occur because of chlamydia.

    00:48 So, psittacosis, which is transmitted by birds, that's why the parrot is there.

    00:54 Is a very common form of lung disease in endemic areas? Trachoma, chlamydia trachomatis, is an eye infection, and is actually the most common cause of blindness in the developing world.

    01:11 And then you can have a even, a venereal form of chlamydia called lymphogranuloma venereum, which is transmitted venereally, and will cause abscess formation and lymphadenopathy in pelvic region.

    01:28 So the pathologic features, again, remember, this is an obligate intracellular pathogen, so the only way that we can really deal with it effectively is to have chronic inflammatory infiltrates such as T cells and NK cells, to try to keep it in check.

    01:43 So that what happens in psittacosis and trachoma.

    01:47 In the lymphogranuloma venereum, we also bring in a substantial component of activated macrophages, and so that's why you get granuloma, this inflammation in that setting.

    01:57 So it's mostly a chronic inflammatory response.

    02:01 Moving further, up the phylogenetic tree, now we're gonna talk about rickettsia.

    02:05 Again, another obligate intracellular bacteria and it is DNA, it's got DNA, it's got RNA, it's got a cell wall.

    02:13 The reason that you're seeing a tick is that it is transmitted by arthropod vectors, so all of the rickettsia, and it will have a particular tropism that gives it it's pathology.

    02:27 Rickettsia likes to go to endothelium and vascular smooth muscle cells so it tends to be a vascular tropic lytic infection, and if you think about it, gee, if a lice endothelial cells, I should get thrombosis, you bet, and that's exactly what happens with rickettsia.

    02:45 So, again, an obligate intracellular pathogen, so we have typically a chronic inflammatory infiltrate when this is around because we can't really deal with it with neutrophils and antibodies and things.

    02:56 It will tend to cause a hemorrhagic vasculitis, and this is the tropism of that bug, it tends to want to go to the endothelial cells and smooth muscle cells.

    03:05 And when you get a lytic infection, then you're gonna get thrombosis, and if you have thrombosis of vessels, the tissue downstream is gonna die so you'll have infarction.

    03:13 The characteristic lesion, so this is demonstrating Rocky Mountain spotted fever, great name for a disease.

    03:20 It's actually not confined to the Rocky Mountains.

    03:23 You can find Rocky Mountain spotted fever all over the world, wherever the rickettsia is.

    03:28 And you get what is called classically palpable purpura, so you can see little areas of bruising on typically the extremities and they are slightly raised, these little areas of focal infarction.

    About the Lecture

    The lecture Infections by Chlamydiae and Rickettsiae by Richard Mitchell, MD, PhD is from the course Host–pathogen Interaction.

    Included Quiz Questions

    1. Trachoma
    2. Aspergillosis
    3. Candidiasis
    4. Dengue
    5. Syphilis

    Author of lecture Infections by Chlamydiae and Rickettsiae

     Richard Mitchell, MD, PhD

    Richard Mitchell, MD, PhD

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