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Lyme disease in Canada: Lyme disease in Canada: modellingmodelling, GIS , GIS and public health actionand public health action

Nick OgdenNick OgdenCentre for Centre for FoodborneFoodborne, Environmental & , Environmental &

ZoonoticZoonotic Infectious DiseasesInfectious Diseases

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Talk Outline

1. Lyme disease in Canada: the issue

2. What public health can do to minimise the risk from Lyme disease

3. How modelling and GIS can help

4. What has been done already and what needs to be done

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Public Health and Zoonoses

Pathogen emerges

Disease in Humans

Recognition & Diagnosis

Response to epidemic

Surveillance/control applied in retrospect (=

too late?)

Riskassessment

Risk specification

ForecastingPrediction

Surveillance

Intervention Human diseaseprevention

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Lyme disease

• A vector-borne zoonosis• Bacterial infection (Borrelia burgdorferi)• Transmitted by ticks from natural wildlife reservoirs accidentally to

humans• Geographic range determined by ticks• Ticks don’t fly

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Lyme disease in Canada: the issue

• Lyme is an environmental health hazard where the environment is suitable for the ticks

• Lyme is endemic in the USA (and Europe and parts of Asia) and in a few localities in Canada

• But the number of localities where Lyme is endemic is increasing in Canada – Lyme is an ‘emerging infectious disease’

• Geographic range of endemic Lyme disease risk is expected to increase with climate change (temperature as well as habitat limits the tick’s range)

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PHAC-led risk assessment: Lyme disease distribution in the USA

I. scapularisI. scapularisI. I. pacificuspacificus

ca 20 000 cases/year in USA = ca 8 000 cases/year in Canadaca 20 000 cases/year in USA = ca 8 000 cases/year in Canada

7Distribution of Distribution of I. scapularisI. scapularis submitted to submitted to PHACPHAC by the publicby the public = migratory bird= migratory bird--borne ticksborne ticks

Ogden et al., (2006) J. Med. Ogden et al., (2006) J. Med. EntomolEntomol

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Reproducing (and selfReproducing (and self--sustaining) sustaining) I. scapularisI. scapularis populations in Canadapopulations in Canada

20081970 1997 2005

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Increasing numbers of human cases

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Cases likely acquired outsideCanada

Cases associated with I. scapularis

Cases associated with I. pacificus

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Cases likely acquired outsideCanada

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What can public health do to minimise the risk from Lyme disease?

• No vaccines available

• Preventable by avoiding tick bites

• Preventable by removing ticks soon after attachment

• Early stages of Lyme recognisable and easily treated

(compared to later disease)

• Effect of Lyme minimised by:

– Educating public about prevention, tick identification and

removal

– Informing doctors of the risk of Lyme, symptoms and

diagnosis

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How can modelling and GIS help public health?

• By predicting when (seasonally and in the future with climate change) and where Lyme disease risk is occurring

• Lyme risk is geographically constrained (temperature, habitat and dispersion of the vector by its hosts)

• Risk maps allow:– Decision making/policies– Targeting of surveillance efforts (some are very

expensive)– Targeting of information regimes: clear need for

targeting preventive messages to risk groups or message exhaustion occurs

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What have we done so far?

• Tick population model to determine temperature limits (Ogden et al., JME 2004; IJP 2005)

• Effects of climate change on geographic limits for tick in Canada (Ogden et al., IJP 2006)

• Analysis of existing surveillance data (Ogden et al., JME 2006a)• Studies on bird dispersion of ticks (Ogden et al., AEM 2008)• Risk maps at provincial-national scale with some field validation

(Ogden et al., Int J. Health Geogr. 2008)• Lyme transmission model and evolutionary processes (Ogden et al

Parasitol 2007, J. Theor. Biol. 2008, Kurtenbach et al., Nature Reviews Microbiol. 2006)

• Initial static habitat suitability maps (Ogden et al., J. Med. Entomol. 2006b) with more detailed study under way

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Risk Maps for Lyme vector: province – national scale

Now 2020s

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Static risk maps at a finer scale (habitat suitability = 30m2)

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To Do:

What habitats/environmental indicators are there on a local scale?How and where do tick vectors and tick-borne pathogens disperse and spread on a within-province scale?How to model it in a way meaningful for public health?

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