Babesia – Protozoa (Hematologic Infection)

by Sean Elliott, MD

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    00:01 Babesia, a parasite.

    00:03 Babesia are protozoan parasites that are transmitted by our friend, ixodes the tick.

    00:11 Why do I say ixodes the tick? Because it is the same tick which can carry Borrelia burgdorferi the cause of lyme disease, so if you've already been through some of the arboviruses or a tick borne infections with bacteria, you know all about the ixodes tick.

    00:28 However in this case we're focusing on it's carriage of Babesia which is a protozoan parasite.

    00:34 Incubation after innoculation with or infection by the babesia takes up to four weeks and there are several important human pathogens which you see listed here: Babesia microti, duncani, divergens, and venatorum.

    00:50 On the image in front of you, you can see highlighted by several dark arrows the appearance of the nuclear material of Babesia as it lives within the erythrocyte, the red blood cell which is its target.

    01:04 So let's look at the pathogenesis of Babesia and like any good parasite it has a certain life cycle.

    01:12 This particular life cycle normally bounces between the ixodes tick as you see on the left and the white footed mouse or perhaps some other cute little rodent which is the other immediate host.

    01:26 The tick is able to introduce through its saliva, a sporozoites through the mouse’s blood stream by taking a blood meal.

    01:37 Within the mouse then those sporozoites go through a binary fission into their first form ultimately becoming gametocytes and then either circulating again in the mouse go into the next stage of differentiation or the tick takes another blood meal, obtains the gametocytes and then also process it inside itself.

    02:04 Regardless of the host, either tick or animal, the gametocytes then process into ray bodies undergo sexual maturation into zygote and ultimately turn back into a sporozoites.

    02:19 Now, that normally should happen back and forth, everything should be fine, honky dory, etc.

    02:24 and so forth, except when the human being gets involved and the human is the one who gets bitten by the tick then everything that happens inside the white footed mouse actually will start to occur inside the human.

    02:36 Not so bad you think, right? Wrong - because that step of binary fission or first replication of the sporozoites going into the gametocyte occurs within the red blood cell giving rise to those dark purple stain material which you saw on the preceding slide and when the gametocytes are ready for the next step they rapture the erythrocyte.

    03:00 So the pathogenesis all has to do with anemia typically hemolytic anemia because those infected erythrocytes will end up being hemolyzed because they have abnormal shape and they're starting to hemolyze or rapture on their own.

    03:17 So when that happens in a progressive fashion and the patient becomes progressively anemic, big surprise clinical manifestation number one: malaise and fatigue - they're anemic so they're very tired.

    03:29 In addition, they have fever and fevers will increase the tempo of the hemolysis of those erythrocytes so the hemolytic aemia goes on even further.

    03:39 Now, if one is immunocompetent, eventually the process will reach some sort of limited control although it’s very difficult to irradicate the infection because again it’s an ongoing parasitic cycle.

    03:53 For those patients who are immunosuppressed, immunocompromised, spleenectomized for whatever reason or at the extremes of age meaning also having less adequate maturity of their immune system, they will have a far more severe process, the hemolytic anemic process and the parasitic cycling will occur in an even greater tempo, they’ll become more anemic faster.

    04:16 So to diagnose Babesiosis, first and most important requires clinical suspicion.

    04:23 In the States, most cases of Babesiosis come from the Eastern Seaboard, however, they can occur sporadically across the United States and throughout the rest of the world.

    04:34 So anemia history of exposure to a tick-rich environment should at least cause the clinician to send a blood smear and request evaluation of the erythrocytes a - or an astute hematopathologist when looking on right stain of that blood smear will see what you see in front of you which are ring forms, the white arrow at the middle of this image or a maltese cross that very characteristic x shape which is to the right side of the slide with the black arrow.

    05:04 To confirm the diagnosis although this picture is pathognomonic of Babesiosis, one could also perform molecular diagnostics with polymerase chain reaction, PCR.

    05:14 After making the diagnosis or even with a tentative diagnosis, treatment can be started with Atovaquone, very similar to what we might treat malaria with, another intraerythrocytic pathogen and also azithromycin, the antibiotic.

    05:29 So Babesia causing Babesiosis, tick associated, a parasitic cycle and a principal cause of hemolytic anemia in a vector associated way.

    About the Lecture

    The lecture Babesia – Protozoa (Hematologic Infection) by Sean Elliott, MD is from the course Parasites.

    Included Quiz Questions

    1. Ixodes
    2. Dermacentor
    3. Amblyomma
    4. Rhipicephalus
    5. Nuttalliella
    1. blood cells.
    2. ...plasma B cells.
    3. ...T helper cells.
    4. ...neutrophils.
    5. ...megakaryocytes.
    1. Maltese cross form in a red blood cell
    2. Giant platelets
    3. Howell-Jolly body
    4. Blister cells
    5. Degmacytes

    Author of lecture Babesia – Protozoa (Hematologic Infection)

     Sean Elliott, MD

    Sean Elliott, MD

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