tularemia in wild rodents and lagomorphs in canada
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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

Tularemia in wild rodents and lagomorphs in Canada

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

slide2

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

slide3

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)

slide4

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
slide5

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)
generally accepted that
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:
sources of data
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
two types of data
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
slide10

Diagnosed occurrence of tularemia

in wild rodents and lagomorphs

slide14

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

tularemia in canada is different than tularemia in usa
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

slide17

Eastern cottontail rabbit

Snowshoe hare

Nuttal’s cottontail rabbit

White-tailed jackrabbit

slide18

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
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
questions
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?
conclusions
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
slide22

“a challenge for the near future

will be the unraveling

of the natural reservoirs

of Francisella tularensis”

(Tärnvik &Berglund, 2003)

slide23

Thank you for

your attention

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