Francisella Tularensis

by Sean Elliott, MD

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    00:01 Francisella tularensis; a bacteria. Francisella is a small gram-negative and aerobic rod such as you see on the stain on the slide on the right.

    00:13 It has very fastidious growth requirements and is in addition, a facultative intracellular bacteria.

    00:22 It does grow slowly, but it can be enriched on a cysteine rich medium.

    00:28 And it is notable for having an anti-phagocytic capsule which in part contributes to its infectivity.

    00:36 Francisella is a bad boy in the bacteria world because it has a very low infectious dose 50 or very low amount of organisms necessary to cause disease in 50% of its targets.

    00:51 Because of that, it is well known to microbiologists and technicians who must undergo special training to handle possible Francisella tularensis culture plates so that they themselves don't become infected.

    01:05 As I said, this is a nasty bad boy.

    01:08 Where does Francisella live? Well, it has multiple natural reservoirs; rabbits, other small warm-blooded animals, ticks, you name it.

    01:18 Transmission can occur via the bite of an infected animal.

    01:24 In case you get bitten by a rabbit sometime, but more commonly being bitten by a tick; a tick taking its blood meal and transmitting the organism.

    01:34 It also can occur via direct contact with the infected animals.

    01:38 And by this, I don't mean simply petting that cute little rabbit.

    01:42 No, that never happens.

    01:43 It actually means being exposed to mucosal surfaces or secretions of the infected animal.

    01:51 A common example would be those who are hunters and skin an infected animal.

    01:57 And in the process of skinning, will actually release or aerosolize the organism.

    02:02 Inhalation of infectious aerosols then - so anything which will vigorously disrupt blood or body fluids and aerosolize that can be another mechanism of transmitting the organism.

    02:14 As a "Eew gross"moment, where I trained in the middle part of the United States, there was something known as tick popping.

    02:23 And this involved picking engorged ticks off dogs or other animals, placing them on a rock and wacking them with another rock.

    02:33 It made a very satisfying pop sound.

    02:35 But unfortunately, those ticks that were also infected with Francisella, aerosolize that organism and those tick poppers as we call them came in with one of the forms of tularemia which we'll talk about in just a second.

    02:50 Note to self: don't skin animals and don't pop ticks.

    02:54 Finally, ingestion of contaminated meat or water is another possible source of acquiring Francisella tularensis.

    03:02 So, a bit about the pathogenesis.

    03:05 As noted before, there is an antiphagocytic capsule which protects the bacteria from being adjusted or phagocytosed by the immune system.

    03:15 It especially grows within the macrophages.

    03:18 When that happens, and again, it can invade the immune system that way.

    03:23 It costs us several well described clinical syndromes.

    03:26 The first is the, sort of the over umbrella term which is tularemia, sometimes nicknamed rabbit fever.

    03:34 Patients suffering with tularemia typically undergo an incubation period of 3 to 5 days after their exposure.

    03:42 And then they develop an abrupt onset of fever along with shaking chills, rigors, malaise and severe fatigue.

    03:50 That maybe no more or no less than a severe form of the flu.

    03:56 But if it is not recognized and treated, it can progress and become quite severe.

    04:01 There also is an ulceroglandular form.

    04:04 Typically, this is in those patients who've been bitten by or inoculated by infected material from an infected source.

    04:12 Typically, patients who develop an ulcerative lesion at the site of their inoculation and that also is the site of their primary infection.

    04:21 You can see an example that on the picture on the right; slight surrounding redness or erythema with an ulcerative lesion at the center.

    04:29 Then, distal to or proximal to, depending on where the infection is, there will be a swelling of the lymph nodes or the glands causing a lymphadenopathy and then glandular fever. Meaning that the fever maybe episodic and spiking at specific times during the day.

    04:50 Then there is another form called oculoglandular form and this is where the organism is in an aerosolized form deposited on to the eye or direct inoculation of the eye.

    05:03 Those patients then develop a very painful conjunctivitis on the side of the inoculation.

    05:09 And if one actually stains or looks more closely at the eye, one can see multiple ulcers within the conjunctivae itself.

    05:17 Those patients will then also have lymphadenopathy or the glandular swelling in the region draining that particular eye.

    05:26 And then there are several other forms as well.

    05:29 Typhoidal which simply is a reference to an overwhelming sepsis with pneumonic, and gastrointestinal depending on whether the patient inhaled potentially the Francisella or ingested, causing the gastrointestinal form. Prevention and treatment.

    05:45 Yes, there's a vaccine. No, it's not commonly available.

    05:50 But yes, if you are at a high risk of being exposed to Francisella such as, you're a veterinarian or a high risk hunter or perhaps a microbiology technician, then the vaccine might be suggested for you.

    06:02 However most often, it is the general person at large who’s exposed to and develops infection from Francisella tularensis.

    06:11 And those are patients who deserve treatment with an antibiotic such as streptomycin or some other aminoglycoside.

    06:18 Typical treatment takes a while; several weeks to get on top of the process and is not always successful. So there is a certain amount of mortality or death rate associated with tularemia.

    06:32 So in looking at Francisella tularensis, the things to remember are; number one, it is highly infectious to the microbiology technician who is trying to culture it.

    06:43 It is associated with - in some cases, tick popping and skinning rabbits.

    06:49 Hence tularemia is called rabbit fever, and it is something which you should really try hard to avoid.

    06:55 And if you do the right things with our friends, the animals, you might be able to.

    About the Lecture

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

    Included Quiz Questions

    1. Gram-negative, facultative, intracellular bacteria
    2. Gram-positive, facultative, extracellular bacteria
    3. Gram-negative, obligate, intracellular bacteria
    4. Gram-positive, obligate, extracellular bacteria
    5. Gram-negative, obligate, extracellular bacteria
    1. Rabbit
    2. Goat
    3. Sheep
    4. Horse
    5. Cow
    1. Tularemia
    2. Whooping cough
    3. Malaria
    4. Typhoid
    5. Scarlet fever
    1. Conjunctivitis
    2. Blepharitis
    3. Sinusitis
    4. Keratoconjunctivitis
    5. Glossitis

    Author of lecture Francisella Tularensis

     Sean Elliott, MD

    Sean Elliott, MD

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