Ixodes scapularisIxodes scapularis & Lyme & Lyme disease spread in Canada: disease spread in Canada:

Climate changeClimate change & & migratory migratory birdsbirds

Nick Ogden

What is Lyme disease?

• A disease caused by a spirochaete bacterium Borrelia burgdorferi

• It is a multisystem disease in humans (and animals)

• It is non-fatal but chronic and debilitating if not treated early

• Difficult to diagnose by doctors (clinical presentation and serology)

• ~ 20 000 cases a year in USA despite high level of awareness by the public & medical practitioners

• It is an infection of wildlife (rodents, birds, mustelids NOT deer) that is transmitted from one animal to another by ticks

• Ticks are not very choosy about who they bite and bite people by accident

• The geographic range of Lyme disease is tied to that of its tick vectors

LarvaLarva ENymphNymph E

Adult Adult E

Eggs

POP

PEP

Borrelia burgdorferi transmission cycleAdult ticks

feed on deer in

spring and autumn

Nymphs feed on rodents and birds in

spring

Infected nymphs infect

rodents or birds

Larvae feed on rodents and birds in late summer

Infected rodents or birds infect

larvae

Infected larvae moult into infected nymphs next spring Tick development and activity depend on temperature

Temperatures are expected to rise dramatically this century: global warming

What’s in store for Canada?Temperature rise:• One of the most seriously affected places on earth• Mean annual surface temperature rises of ca 4ºC in

southern Ontario/Quebec, up to 10ºC in NunavutChange in rainfall:• Slight increase in rain in the east? Reduced rain in the

prairies and the west• Change in pattern: heavy rainfall events accompanied by

flooding interspersed by droughtsThe greater the mitigation, the less severe the effects, hence

Kyoto• General expectation that the geographic range of

arthropods (such as ticks) will expand north with global warming

Where are the ticks now:

In the USA!

Ixodes scapularisIxodes pacificus

For Lyme to more seriously affect Canada the range of I. scapularis would have to expand

In Canada we have only a few reproducing (and self-sustaining) I. scapularis populations

Adult I. scapularis ticks are already submitted to Health Canada by the public from a very wide geographic range: How come?

We hypothesize that migratory ground-feeding birds are bringing I. scapularis into, and through,

Canada

Northern-migrating ground-feeding birds stop-

over in tick-infested habitatSpring migration

coincides with spring activity

period of Ixodes scapularis nymphs

Nymphs feed continuously on birds for 5 days, then drop off into the habitat

Why study ticks on migratory birds?• Many nymphal ticks carried by migratory birds survive and

molt into adult ticks, which can bite people and infect them with Lyme disease.

• Understanding the distribution of these ticks will help alert health workers and the public as to where the risks are from these ticks

• Reproducing (established) tick populations carry much risk more because:– The ticks are more numerous– Nymphal ticks are present, which are highly infected, difficult to see and

more likely to infect people than adult ticks

• With global warming we expect that the range of reproducing populations of ticks to expand

• Where ticks are being dropped in the greatest numbers by the birds now is where populations are likely to establish

We have developed a simulation model of I. scapularis populations to identify where temperature conditions

are OK for I. scapularis

0 1-4647-90

91-159

160-266

267-433

434-694

695-1101

1102-1738

1739-2145

Now:

Index of tick abundance at model equilibrium

0 1-4647-90

91-159

160-266

267-433

434-694

695-1101

1102-1738

1739-2145

And forecast for e.g. 2020

Index of tick abundance at model equilibrium

The range of I. scapularis may continue to expand through this century

Now

2020s

2050s

2080s

Our research conclusions so far are:

• A northward expansion of the range of Ixodes scapularis, associated with climate change, is likely because:

– Tick survival increases dramatically

– Ticks are being carried into Canada each year on migratory birds

– The habitat in many areas is suitable for tick survival

• Chaotic weather (heavy rainfall and droughts) may inhibit spread

• Spread into central Provinces may be limited by low rainfall

• Diagnostic expertise by clinicians and laboratories will be crucial in detecting and monitoring the increased risk of Lyme disease

• We can help by identifying where ticks are landing now, and thus where tick populations may set up in the future

The role of migratory birds: what we need to know

1. What bird species are responsible for carrying ticks into Canada:

– What species carry ticks (finding ticks on birds)– How many ticks are carried, on average, by each individual bird

(counting and collecting ticks)– How abundant the birds are (banding records)

2. Where these birds are going:– From analysis of isotopes in retrices– Banding recoveries– Ecological niche modeling

3. Where the ticks are going:– Using the above data in simulation models (‘network analysis’:

equivalent to methods used by airlines to estimate where passengers get on and off planes)

– Existing maps of I. scapularis distribution in the USA (CDC)– Range of 5 days flying time for Nymph, 3 days for a Larva

A basic model of tick dispersion by migratory birds

Number of ticksdropping onlocation Xin Canada

Number of ticksQuesting in

USA woodlandin spring

5 days flight time

1971-2000

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1 2 3 4 5 6 7 8 9 10 11 12

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Depends on phenology of tickwhich depends on climate

Numbers of ticks carried per bird

Number of ticksdropping onlocation Xin Canada

Number of ticksQuesting in

USA woodlandin spring

5 days flight time

Species: timing of migration

Species: behaviour contacting ticks

Species: migration route

Species: speed of migration

Bird behaviour and contact with Ixodes scapularis: A meta-analysis of previous

studies

• Data from 15 studies on I. scapularis infestations of birds (migrating and resident) in the USA and Canada

• Negative binomial regressions with outcome = number of birds infested and number examined as an offset

• Explanatory variables: foraging behaviour, nesting site, habitat and ‘taxonomic groupings’. Study ID was a random effect

• Significant factors +ve association with parasitism: ground feeding behaviour, ground nesting, woodland/ecotone habitat and some family groupings

Species selected by meta-analysis

• Corvids: Blue Jay• Sparrows: Eastern Towhee, Chipping Sparrow, Song

Sparrow, Swamp Sparrow• Icterids: Brown-headed Cowbird, Common Grackle• Mimids: Brown Thrasher, Grey Catbird• Tanagers: Northern Cardinal• Thrushes: American Robin, Veery, Grey-cheeked,

Hermit, Swainson’s & Wood Thrushes• Warblers: Worm-eating, Hooded & Canada Warblers,

Ovenbird, Northern Waterthrush, Common Yellowthroat• Wrens: House Wren

Coincidence of migration with tick questing

1971-2000

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35o

40o

42.5o

Common YellowthroatAmerican robin

Data from the field: Spring migration 2005 in Canada

• Corvids: Blue Jay 4• Sparrows: Eastern Towhee 2, Chipping Sparrow 2, Song Sparrow

13, Swamp Sparrow 7 (WT WC ST Fox GH Lincoln 43)• Icterids: Brown-headed Cowbird 1, Common Grackle 2• Mimids: Brown Thrasher 14, Grey Catbird 4• Tanagers: Northern Cardinal 1• Thrushes: American Robin 2, Veery 2, Grey-cheeked 2, Hermit 21,

Swainson’s 3 & Wood Thrushes• Warblers: Worm-eating, Hooded & Canada Warblers, Ovenbird 3,

Northern Waterthrush, Common Yellowthroat 3• Wrens: House Wren 9+ BC chickadee 1, Black & white warbler 1, Black-throated blue warbler 1, Magnolia warbler

1, Nashville warbler 1, Yellow warbler 1, RC Kinglet 2, Starling 2, RW Blackbird 9

AcknowledgementsThe team:• Bird Studies Canada:

– Audrey Heagy• Canadian Wildlife Service

– Charles Francis• Saint-Hyacinthe, QC:

– Alex Thompson (Université de Montréal)– Michel Bigras-Poulin (Université de Montréal)

• Kingston, ON:– Chris O’Callaghan (Queens University)

• Toronto, ON:– Abdel Maarouf (Environment Canada, York University)

• Guelph, ON:– Dominique Charron (Public Health Agency of Canada)– Ian Barker (University of Guelph)

• Winnipeg, MB:– Robbin Lindsay (Public Health Agency of Canada)

Funding by NRC Climate Change Impacts & Adaptations Programme