Lyme disease in Canada: modelling,, GIS and public health action

Transcription

1 1 Lyme disease in Canada: modelling,, GIS and public health action Nick Ogden Centre for Foodborne,, Environmental & Zoonotic Infectious Diseases

2 2 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

3 3 Public Health and Zoonoses Pathogen emerges Disease in Humans Recognition & Diagnosis Response to epidemic Surveillance/control applied in retrospect (= too late?) Forecasting Prediction Risk assessment Risk specification Intervention Human disease prevention Surveillance

4 4 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

5 5 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)

6 PHAC-led risk assessment: Lyme disease distribution in the USA 6 ca cases/year in USA = ca cases/year in Canada I. pacificus I. scapularis

7 Distribution of I. scapularis submitted to PHAC by the public = migratory bird- borne ticks 7 Ogden et al., (2006) J. Med. Entomol

8 8 Reproducing (and self-sustaining) sustaining) I. scapularis populations in Canada

9 Increasing numbers of human cases 35 I Cases scap associated with I. scapularis I Cases pac associated with I. pacificus Cases likely acquired outside Canada 0 9 Number of reported cases Pre

10 10 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

11 11 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

12 12 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

13 13 Risk Maps for Lyme vector: province national scale Now 2020s

14 Static risk maps at a finer scale (habitat suitability = 30m 2 ) 14

15 15 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? Diffusion, cellular automata, network analysis a) b)