by Sean Elliott, MD

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    00:01 Borrelia, a bacteria. Borrelia are another example of spirochetes.

    00:07 These are probably one of the larger types of spirochetes that we know about in human science, certainly larger than treponemes, the cause of syphilis, yaws, and pinta.

    00:17 The Borrelia however possess numerous axial filaments unlike other types of spirochetes that have one to three, they are microaerophilic and they’re very difficult to culture.

    00:30 In fact, as we’ll talk about in a little bit, they can mostly be diagnosed via dark field microscopy such as you see on the image on this slide or by serologic or antibody reactions to confirm an immunologic reaction to them.

    00:45 Today, we’re gonna talk about the two principal human pathogens, that being Borrelia burgdorferi and Borrelia recurrentis.

    00:54 Borrelia burgdorferi is the cause of Lyme disease and as such, it is the target of intense human scrutiny and sometimes, an overabundance of clinical interest. Lyme disease, Borrelia burgdorferi which is common in the Northeastern United States.

    01:12 I should point out that colorful slide or colorful image on the preceding slide was a whole bunch of Borrelia piled up on top of each other, those spirochetal structures making it look almost like a sponge.

    01:25 That doesn’t necessarily occur in nature but it certainly made for a beautiful image.

    01:30 This image is not so beautiful.

    01:32 This is a picture of the United States and every dark purple spot that you see is a representation of a county with a reported case of Lyme disease.

    01:43 As you can see, Lyme disease certainly appears to predilect in the Northeastern part of the country but there are dark purple dots all over every single state. Most of those represent cases that were imported, meaning, acquired from an endemic part of the country, the North sea, Northeastern part, and then, a returning traveler going back home and then, developing the clinical symptoms someplace else.

    02:10 The reservoir for Borrelia is the white footed mouse and then, also in deer and we’ll talk about the natural life cycle coming up very shortly.

    02:19 The transmission however is the ixodes scapularis tick otherwise known as the black legged tick or the deer tick and this image shows an engorged tick, quite an unreasonable looking beast.

    02:33 He’s certainly not something that you would like to discover stuck to your arm or other parts.

    02:38 Let’s look now at the lifecycle of Borrelia burgdorferi as pertains to the lifecycle of the tick, its primary vector or host.

    02:48 And I’ll point out at the start of this slide that this entire cycle takes over three years, two and a half or three years, the time it takes for an egg to mature into an adult tick.

    02:57 the time it takes for an immature or an egg to mature into an adult tick.

    02:58 the time it takes for an immature or an egg to mature into an adult tick.

    03:01 We’ll start off then on the left lower part of the slide with an adult female tick dropping off its eggs.

    03:07 Those eggs will mature into six legged larvae that soon after this maturation will start looking for their first blood meal.

    03:16 That meal typically occurs from a small rodent, especially our friend, the mouse, and it is from that mouse or whatever rodent that the larvae may first acquire Borrelia burgdorferi.

    03:29 At this time however, they are not yet ready to attack or ingest, and transfer Borrelia to a human being.

    03:33 At this time however, they are not yet ready to transfer Borrelia to a human being.

    03:36 Next, over the following season, the winter months, the larvae will molt and when they emerge from the winter into the spring, they will have molted into nymphs and this means that they are now hungry and looking for their second blood meal, their second feast if you will.

    03:55 Here, most often, the nymphs will actually take their second meal from another warm-blooded mammal.

    04:04 It may be a larger one, it may still yet be the mouse.

    04:07 The picture here shows a raccoon and they also may acquire Borrelia burgdorferi from this second animal host.

    04:15 Then, we go through another year, another winter season at which point, the nymphs are growing and eventually, maturing into adults and at this point, they are ready for their third and final blood meal which may be from a larger animal.

    04:31 They’re bigger, they can live higher up, they can drop from forest leaves, or trees, or branches onto a taller creature such as a deer or some other hooved animal.

    04:43 However, there are several points at which the tick in its very stages can transmit Borrelia burgdorferi to the human being.

    04:51 The first is as a nymph.

    04:54 Meaning, it’s survived its first winter, it’s turned into the second stage of the tick and it’s looking for a second blood meal.

    05:01 If that nymph was previously infected from its mouse host the last season with Borrelia, it can then transmit Borrelia to the human being by taking a second blood meal.

    05:13 Similarly, the adult can transmit Borrelia to either a human or a human’s best friend, the dog as you see there while on a camping trip or hiking through who knows where.

    05:25 So, two stages at which the organism itself can be transmitted to the human being.

    05:32 So, following that inoculation, that injection of Borrelia burgdorferi into the human being via the bite of an infected tick either at the nymph session, the nymph status, or the adult status, then, the bacteria enters the bloodstream through the skin, through that bite and it spreads to multiple organs and the image here on the right shows anywhere from the heart, to the lungs, to the kidneys, the liver, you name it.

    06:01 This is where primary infection can absolutely occur driving then an immune response followed by disease manifestations.

    06:09 The principal clinical symptoms and signs of Lyme disease are absolutely caused by the human’s immune reaction to Borrelia burgdorferi, not specifically from any action of Borrelia burgdorferi, although, it does as you see here express a very weak endotoxin-like activity.

    About the Lecture

    The lecture Borrelia by Sean Elliott, MD is from the course Bacteria.

    Included Quiz Questions

    1. Lyme disease
    2. Sickle cell disease
    3. Addison disease
    4. Celiac disease
    5. Graves disease
    1. White-footed mouse
    2. Mosquito
    3. Goat
    4. Sheep
    5. Cow
    1. 3 years
    2. 3 months
    3. 6 weeks
    4. 3 weeks
    5. 6 months
    1. Nymph and adult stages
    2. Nymph and larval stages
    3. Adult and larval stages
    4. Larval and egg stages
    5. Nymph and egg stages

    Author of lecture Borrelia

     Sean Elliott, MD

    Sean Elliott, MD

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