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.

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

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)

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

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: n Type A is associated with lagomorphs and tick or biting fly transmission n Type B is associated with rodents and water transmission but also occurs in terrestrial situations

Farlow et al. 2005 Emerging Infectious Diseases 11(12)

Sources of data n n n 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 n n Cases diagnosed in wild rodents or lagomorphs (retrospective IHC on some suspect cases) Human cases in which an animal source is described

Diagnosed occurrence of tularemia in wild rodents and lagomorphs BC Beaver Muskrat Snowshoe hare Richardson’s ground squirrel Deer mouse House mouse White-tailed jackrabbit Franklin’s ground squirrel Microtus spp. “rabbit” AB SK MB ON QC NB NS PE NF NT YU

Human disease associated with wild rodents/lagomorphs BC Beaver Muskrat Snowshoe hare Groundhog Ground squirrel Deer mouse Red squirrel Microtus spp. Rodents on farm “rabbit” “squirrel” AB SK MB ON QC NB NS PE NF NT YU

Proportion of cases diagnosed in major species

Proportion of human cases associated with major species

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? 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

Snowshoe hare White-tailed jackrabbit Eastern cottontail rabbit Nuttal’s cottontail rabbit

Snowshoe hare White-tailed jackrabbit Eastern cottontail Nuttall’s cottontail

Snowshoe hares occur in northern states and cottontails occur in ON, QC, MB, SK, AB and BC BUT: n n 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 n Why don’t we not see tularemia in cottontail rabbits or tick-transmitted disease in humans? n Where do various subspecies and subtypes of F. tularensis occur in Canada? n What are the reservoirs of terrestrial tularemia? n What type of F. tularensis occurs in snowshoe hares and what effect does it have? n Why don’t we see tularemia in ground squirrels or jackrabbits?

Conclusions n n n 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

“a challenge for the near future will be the unraveling of the natural reservoirs of Francisella tularensis” (Tärnvik &Berglund, 2003)

Thank you for your attention