Transcript Document
Journal Club of Veterinary Medicine Climate Change and the Potential Range Expansion of the Lyme Disease Vector Ixodes scapularis in Canada April 2007 Presented by Brian Lassen Ph.d student Estonian University of Life Sciences Ogden NH, Maarouf A, Barker IK, BigrasPoulin M, Lindsay LR, Morshed MG, O’Callaghan CJ, Ramay F, WaltnerToews D, Charron DF International Journal of Parasitology, 36 (2006) 63-70 Why? Mean annual temperature Mean air temp. Tartu 1866-2000 Why? Is Lyme disease a growing problem? 5000 Cases of Lyme borreliosis 4500 4000 3500 Finland 3000 Estonia 2500 Latvia 2000 Lithuania Poland 1500 1000 500 0 2001 2002 2003 2004 2005 Year Smith R,Takkin J, Lyme borreliosis: Europe-wide coordinated surveillance and action needed?, Eurosurveillance (2006) vol 11 (6) Latitude orientaiton World Climate World average rainfall Forrest Life Cycle of Ixodes scapularis Model design (Ogden et al. 2005) Eggs μe Daily, per-capita mortality rate of eggs (0.002) ELAt−y Number of egg-laying adult females at time t−y (initial value 0) Et−q Number of eggs at time t−q (initial value 0) q Time delay for the pre-eclosion period of eggs (34,234×[Temperature−2.27]) Mean annual degree days >00C (DD >00C) Project Objectives 1. Gegeographical range increasements? 2. Reduction in threshold of immigrating ticks? 3. Seasonal timing = endimic cycles of tick pathogens Methods Objective: Geographical distribution of ticks Tool: Maps on Ogdens model (2005) for DD >00C 2020 2050 2080 Methods Objectives: Northern limits of tick survial Northern edge seasonal tick activity period Tool: Population model Ogdens (2005) Location: four sites in Ontario Canada Methods DD >00C map CGCM2 HadCM3 + atmosphere-ocean interaction Daily min/max/mean Mean annual DD >00C Methods DD >00C under climate change scenarios Scenarios CGCM2 A2 (pesimistic/realistic) HadCM3 B2 (optimistic) Plotting of map lines: With and without temperature adjustments for great water bodies Methods Theoretical limit for I. scapularis establishment Annual maximum number of adult ticks at model equilibrium y Tick die out Tested on historical data from 12 meterological stations for calibration x DD >00C from Canadian meterological stations Results Simulated maximum increase of annual adult ticks with DD>00C increase Fig.2 Objective 2 Ontario Wiarton ▲ Timmins ■ Picton ○ Chatham 2875 DD>00C Less water surface cooling inlands Northern locations less likely to be affected by water surface cooling Results Theoretical limits for I. scapularis establishment at climate change scenarios Fig.1 Objective 1 Non-cooled Cooled B2 lower Results Seasonal tick survival under climate change scenarios Fig.3 Objective 3 Larvae Nymphal Adult Cantham, Ontario Established tick population CGCM2 model A2 emission Timmins, Ontario No current tick population Results Fig.3 Seasonal tick survival under climate change scenarios Lower annual mortality Objective 3 Larvae Nymphal Faster development More ticks over time Adult Earlier activity period Longer activity period CGCM2 model A2 emission Discussion Model limitations Depends on host finding success DD>00C is limited as projection: Mean DD>00C flawed for local seasonal variations on survival Insensitve to arid habitats (prairies) limiting spread Insensitive to local rainfall variations and humidity Stochastic extinsions of ticks Conflict with Brownstein et al. 2005 (lower border projections) Correlation with USA data on borders to Canada Discussion Thoughts Disease mostly southern problem (population density) Migrating birds may spread ticks (range extention) Changes leads to deer incresement in rodent areas (reservoirs) Forests will also expand with climate change (habitats) Discussion Conclusions Historical correlation (good model) Realistic that I. scapularis populations will establish northwards Double by 2020 With temperature increase larvae are active and feed earlier Transmission and rain models needed NEXT JOURNAL CLUB IS THE 17th MAY 2007 PRESENTERS NEEDED!