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Risk maps for range expansion of the Lyme disease vector, Ixodes scapularis, in Canada now and with climate change

Nicholas H Ogden12*, Laurie St-Onge3, Ian K Barker4, Stéphanie Brazeau3, Michel Bigras-Poulin2, Dominique F Charron5, Charles M Francis6, Audrey Heagy7, L Robbin Lindsay8, Abdel Maarouf9, Pascal Michel3, François Milord10, Christopher J O'Callaghan11, Louise Trudel12 and R Alex Thompson13

Author Affiliations

1 Centre for Food-borne, Environmental and Zoonotic Infectious Diseases, Public Health Agency of Canada, Saint-Hyacinthe, Québec, Canada

2 Groupe de recherche en épidémiologie des zoonoses et santé publique, Faculté de médecine vétérinaire, Université de Montréal, Saint-Hyacinthe, Québec, Canada

3 Laboratory for Foodborne Zoonoses, Public Health Agency of Canada, Saint-Hyacinthe, Québec, Canada

4 Canadian Cooperative Wildlife Health Centre, Department of Pathobiology, University of Guelph, Guelph, Ontario, Canada

5 International Development Research Centre, Ottawa, Ontario, Canada

6 Migratory Bird Populations Division, Canadian Wildlife Service, Environment Canada, Ottawa, Ontario, Canada

7 Bird Studies Canada, Port Rowan, Ontario, Canada

8 Special Pathogens Division, Public Health Agency of Canada, National Microbiology Laboratory, Winnipeg, Manitoba, Canada

9 Adaptations and Impacts Research Group, Meteorological Service of Canada, Environment Canada, Canada (Now retired)

10 Institut national de santé publique du Québec, Longueuil, Québec, Canada

11 Department of Community Health and Epidemiology, Queen's University, Kingston, Ontario, Canada

12 Laboratoire de santé publique du Québec, Institut national de santé publique du Québec, Sainte-Anne-de-Bellevue, Québec, Canada

13 National Surveillance Unit, Centers for Epidemiology and Animal Health USDA APHIS/Veterinary Services, Fort Collins, Colorado, USA

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International Journal of Health Geographics 2008, 7:24  doi:10.1186/1476-072X-7-24

Published: 22 May 2008

Abstract

Background

Lyme disease is the commonest vector-borne zoonosis in the temperate world, and an emerging infectious disease in Canada due to expansion of the geographic range of the tick vector Ixodes scapularis. Studies suggest that climate change will accelerate Lyme disease emergence by enhancing climatic suitability for I. scapularis. Risk maps will help to meet the public health challenge of Lyme disease by allowing targeting of surveillance and intervention activities.

Results

A risk map for possible Lyme endemicity was created using a simple risk algorithm for occurrence of I. scapularis populations. The algorithm was calculated for each census sub-division in central and eastern Canada from interpolated output of a temperature-driven simulation model of I. scapularis populations and an index of tick immigration. The latter was calculated from estimates of tick dispersion distances by migratory birds and recent knowledge of the current geographic range of endemic I. scapularis populations. The index of tick immigration closely predicted passive surveillance data on I. scapularis occurrence, and the risk algorithm was a significant predictor of the occurrence of I. scapularis populations in a prospective field study. Risk maps for I. scapularis occurrence in Canada under future projected climate (in the 2020s, 2050s and 2080s) were produced using temperature output from the Canadian Coupled Global Climate Model 2 with greenhouse gas emission scenario enforcing 'A2' of the Intergovernmental Panel on Climate Change.

Conclusion

We have prepared risk maps for the occurrence of I. scapularis in eastern and central Canada under current and future projected climate. Validation of the risk maps provides some confidence that they provide a useful first step in predicting the occurrence of I. scapularis populations, and directing public health objectives in minimizing risk from Lyme disease. Further field studies are needed, however, to continue validation and refinement of the risk maps.