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Tularemia in wild rodents and lagomorphs in Canada. Gary Wobeser, Canadian Cooperative Wildlife Health Centre, Department of Veterinary Pathology, U of Sask. “ Few, if any zoonotic diseases have a broader or more complex host distribution and epizootiology” (Petersen & Schriefer, 2005).

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Tularemia in wild rodents and lagomorphs in Canada

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Tularemia in wild rodents and lagomorphs in canada l.jpg

Tularemia in wild rodents and lagomorphs in Canada

Gary Wobeser, Canadian Cooperative Wildlife Health Centre, Department of Veterinary Pathology, U of Sask.


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“Few, if any zoonotic diseases have a broader or more complex host distribution and epizootiology” (Petersen & Schriefer, 2005)


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1911 a “plague-like disease” in California ground squirrels

1912 Bacterium tularense isolated

1914 human disease associated with cottontail rabbits (“rabbit fever”) and later with deerfly bites (“deerfly fever)


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  • 1929 human, Timmins, ON in association with snowshoe hares

  • 1930 sick snowshoe hare at Vavenby, BC

  • 1931-1940 flurry of human cases in AB associated with “rabbits”

  • 1938 F. tularensis isolated from Dermacentor andersoni in AB

  • 1940-42 domestic sheep in AB (2 human cases, jackrabbit, ground squirrel), many D. andersoni

  • 1952-53 beaver and muskrat (Waterton Lakes National Park, AB)

  • 2005 outbreak in deer mice in SK


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    • Francisella tularensis (4 subspecies):

      • F. t. tularensis (type A tularemia)*

      • F. t. holarctica (type B tularemia)*

      • F. t. mediaasiatica

      • F. t. novicida

    • two subtypes of F.t. tularensis :

      • A I (A east): lower elevations, eastern cottontail rabbit, Amblyoma americanum, D. variabilis high virulence (human)

      • A II (A west): higher elevations, Nuttall’s cottontail??, D. andersoni, Chrysops discalis , very low virulence (human)


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    Type A is associated with lagomorphs and tick or biting fly transmission

    Type B is associated with rodents and water transmission but also occurs in terrestrial situations

    Generally accepted that:


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    Farlow et al. 2005 Emerging Infectious Diseases

    11(12)


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    Sources of data

    • CCWHC data base

    • Records of veterinary colleges pre-CCWHC

    • Provincial veterinary laboratories

    • Provincial and territorial wildlife disease specialists

    • Published literature

    • Public Health Agencies


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    Two types of data

    • Cases diagnosed in wild rodents or lagomorphs (retrospective IHC on some suspect cases)

    • Human cases in which an animal source is described


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    Diagnosed occurrence of tularemia

    in wild rodents and lagomorphs


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    Human disease associated with wild rodents/lagomorphs


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    Proportion of cases diagnosed in major species


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    Proportion of human cases associated with major species


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    Tularemia identified more commonly in beaver than in muskrats or snowshoe hares, but hares and muskrats are more common source of human infection

    Beaver larger and more valuable,

    more likely to be submitted to laboratory

    More people handle more muskrats and

    snowshoe hares


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    Tularemia in Canada is different than tularemia in USA?

    Human tularemia is a rare disease in Canada, e.g., prior to 1970, 220 cases in Canada vs. 33,089 cases in USA

    >90% of human cases in USA are tick-transmitted; tick transmission to humans is rare in Canada

    Different “rabbits” are associated with tularemia


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    Eastern cottontail rabbit

    Snowshoe hare

    Nuttal’s cottontail rabbit

    White-tailed jackrabbit


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    Eastern

    cottontail

    Snowshoe

    hare

    White-tailed

    jackrabbit

    Nuttall’s

    cottontail


    Snowshoe hares occur in northern states and cottontails occur in on qc mb sk ab and bc but l.jpg

    Snowshoe hares occur in northern states and cottontails occur in ON, QC, MB, SK, AB and BC BUT:

    • Tularemia very common in cottontails but rare in snowshoe hares in USA

    • Tularemia relatively common in snowshoe hares in Canada but never diagnosed in cottontails in Canada

    • Human infection associated with cottontails in USA but no record in Canada

    • Human infection commonly associated with snowshoe hares in Canada, very rarely in USA


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    Questions

    • Why don’t we not see tularemia in cottontail rabbits or tick-transmitted disease in humans?

    • Where do various subspecies and subtypes of F. tularensis occur in Canada?

    • What are the reservoirs of terrestrial tularemia?

    • What type of F. tularensis occurs in snowshoe hares and what effect does it have?

    • Why don’t we see tularemia in ground squirrels or jackrabbits?


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    Conclusions

    • Tularemia is not a simple or a single disease

    • Overlapping cycles of different subspecies and subtypes of F. tularensis, different animals, various arthropods, water

    • the true reservoirs are unknown


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    “a challenge for the near future

    will be the unraveling

    of the natural reservoirs

    of Francisella tularensis”

    (Tärnvik &Berglund, 2003)


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    Thank you for

    your attention


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