Tularemia in wild rodents and Tularemia in wild rodents and lagomorphs in Canadalagomorphs in Canada

Gary Wobeser, Canadian Gary Wobeser, Canadian Cooperative Wildlife Health Cooperative Wildlife Health

Centre, Department of Veterinary Centre, Department of Veterinary Pathology, U of Sask.Pathology, U of Sask.

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

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

1912 1912 Bacterium tularenseBacterium tularense isolated isolated

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

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

1930 sick snowshoe hare at Vavenby, BC 1930 sick snowshoe hare at Vavenby, BC 1931-1940 flurry of human cases in AB associated 1931-1940 flurry of human cases in AB associated with “rabbits” with “rabbits” 1938 F. tularensis1938 F. tularensis isolated from isolated from Dermacentor Dermacentor andersoniandersoni in AB in AB1940-42 domestic sheep in AB (2 human cases, 1940-42 domestic sheep in AB (2 human cases, jackrabbit, ground squirrel), many jackrabbit, ground squirrel), many D. andersoniD. andersoni1952-53 beaver and muskrat (Waterton Lakes 1952-53 beaver and muskrat (Waterton Lakes National Park, AB)National Park, AB)2005 outbreak in deer mice in SK2005 outbreak in deer mice in SK

Francisella tularensis (Francisella tularensis (4 4 subspecies):subspecies):

F. t. tularensisF. t. tularensis (type A tularemia)* (type A tularemia)*F. t. holarcticaF. t. holarctica (type B tularemia)* (type B tularemia)*F. t. mediaasiaticaF. t. mediaasiaticaF. t. novicidaF. t. novicida

two subtypes of two subtypes of F.t. tularensisF.t. tularensis : :A I (A east): lower elevations, eastern A I (A east): lower elevations, eastern cottontail rabbit, cottontail rabbit, Amblyoma americanumAmblyoma americanum, , D. D. variabilis variabilis high virulence (human)high virulence (human)A II (A west): higher elevations, Nuttall’s A II (A west): higher elevations, Nuttall’s cottontail??, cottontail??, D. andersoniD. andersoni, , Chrysops discalis , Chrysops discalis , very low virulence (human)very low virulence (human)

Generally accepted that:Generally accepted that:

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

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

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

Sources of dataSources of data

CCWHC data baseCCWHC data base Records of veterinary colleges pre-Records of veterinary colleges pre-

CCWHCCCWHC Provincial veterinary laboratoriesProvincial veterinary laboratories Provincial and territorial wildlife disease Provincial and territorial wildlife disease

specialistsspecialists Published literaturePublished literature Public Health AgenciesPublic Health Agencies

Two types of dataTwo types of data

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

Human cases in which an animal Human cases in which an animal source is describedsource is described

BCBC ABAB SKSK MMBB

OONN

QCQC NBNB NSNS PEPE NFNF NTNT YUYU

BeaverBeaver

MuskratMuskrat

Snowshoe hareSnowshoe hare

Richardson’s Richardson’s ground squirrelground squirrel

Deer mouseDeer mouse

House mouseHouse mouse

White-tailed White-tailed jackrabbitjackrabbit

Franklin’s ground Franklin’s ground squirrelsquirrel

MicrotusMicrotus spp. spp.

““rabbit”rabbit”

Diagnosed occurrence of tularemia in wild rodents and lagomorphs

BCBC ABAB SKSK MMBB

OONN

QCQC NBNB NSNS PEPE NFNF NTNT YUYU

BeaverBeaver

MuskratMuskrat

Snowshoe hareSnowshoe hare

GroundhogGroundhog

Ground squirrelGround squirrel

Deer mouseDeer mouse

Red squirrelRed squirrel

Microtus Microtus spp. spp.

Rodents on farmRodents on farm

““rabbit”rabbit”

““squirrel”squirrel”

Human disease associated with wild rodents/lagomorphs

beaver

muskrat

SS hare

Gr. Sq

Proportion of cases diagnosed in major species

beavermuskratSS hareGr. Sq.

Proportion of human cases associated with major species

Tularemia identified more Tularemia identified more commonly in beaver than in commonly in beaver than in muskrats or snowshoe hares, muskrats or snowshoe hares, but hares and muskrats are but hares and muskrats are

more common source of more common source of human infectionhuman 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 Tularemia in Canada is different than tularemia in different than tularemia in

USA?USA?

Human tularemia is a rare disease in Canada, Human tularemia is a rare disease in Canada, e.g., prior to 1970, 220 cases in Canada vs. e.g., prior to 1970, 220 cases in Canada vs. 33,089 cases in USA33,089 cases in USA

>90% of human cases in USA are tick->90% of human cases in USA are tick-transmitted; tick transmission to humans is rare in transmitted; tick transmission to humans is rare in CanadaCanadaDifferent “rabbits” are associated with tularemia

Snowshoe hare Eastern cottontail rabbit

White-tailed jackrabbit Nuttal’s cottontail rabbit

Snowshoe hare

Eastern cottontail

White-tailed jackrabbit

Nuttall’s cottontail

Snowshoe hares occur in Snowshoe hares occur in northern states and cottontails northern states and cottontails

occur in ON, QC, MB, SK, AB occur in ON, QC, MB, SK, AB and BC BUT:and BC BUT:

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

Tularemia relatively common in snowshoe Tularemia relatively common in snowshoe hares in Canada but hares in Canada but nevernever diagnosed in diagnosed in cottontails in Canadacottontails in Canada

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

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

QuestionsQuestions Why don’t we not see tularemia in cottontail rabbits Why don’t we not see tularemia in cottontail rabbits

or tick-transmitted disease in humans?or tick-transmitted disease in humans?

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

What are the reservoirs of terrestrial tularemia?What are the reservoirs of terrestrial tularemia?

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

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

ConclusionsConclusions

Tularemia is not a simple or a single Tularemia is not a simple or a single disease disease

Overlapping cycles of different Overlapping cycles of different subspecies and subtypes of subspecies and subtypes of F. F. tularensistularensis, different animals, various , different animals, various arthropods, waterarthropods, water

the true reservoirs are unknown the true reservoirs are unknown

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

Thank you for your attention