Presented by Brian Lassen
Ph.d student
Estonian University of Life Sciences
Climate Change and the Potential Range Expansion of the Lyme Disease Vector Ixodes scapularis in Canada
International Journal of Parasitology, 36 International Journal of Parasitology, 36 (2006) 63-70(2006) 63-70
Ogden NH, Maarouf A, Barker IK, Bigras-Ogden NH, Maarouf A, Barker IK, Bigras-Poulin M, Lindsay LR, Morshed MG, Poulin M, Lindsay LR, Morshed MG, O’Callaghan CJ, Ramay F, Waltner-O’Callaghan CJ, Ramay F, Waltner-
Toews D, Charron DFToews D, Charron DF
Journal Club of Veterinary Medicine
April 2007
Why?
Mean air temp. Tartu 1866-2000
Mean annual temperature
Why?
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2001 2002 2003 2004 2005
Year
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yme
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Estonia
Latvia
Lithuania
Poland
Smith R,Takkin J, Lyme borreliosis: Europe-wide coordinated surveillance and action needed?, Eurosurveillance (2006) vol 11 (6)
Is Lyme disease a growing problem?
Latitude orientaiton
World Climate
World average rainfall
Forrest
Life Cycle of Ixodes scapularis
Model design (Ogden et al. 2005)
Mean annual degree days >00C (DD >00C)
Eggsμe 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])
Project Objectives
1. Gegeographical range increasements?
2. Reduction in threshold of immigrating ticks?
3. Seasonal timing = endimic cycles of tick pathogens
Tool: Maps on Ogdens model (2005) for DD >00C
2020 2050 2080
Objective:
Geographical distribution of ticks
Methods
Tool: Population model Ogdens (2005)
Objectives:
Northern limits of tick survial
Northern edge seasonal tick activity period
Location: four sites in Ontario Canada
Methods
DD >00C map
Daily min/max/mean
Mean annual DD >00C
CGCM2
HadCM3
+ atmosphere-ocean interaction
Methods
DD >00C under climate change scenarios
CGCM2
HadCM3
Scenarios
A2 (pesimistic/realistic)
B2 (optimistic)
Plotting of map lines:
With and without temperature adjustments for great water bodies
Methods
MethodsTheoretical limit for I. scapularis establishment
Annual maximum number of adult ticks at model equilibrium
DD >00C from Canadian meterological stations
Tick die out
x
y
Tested on historical data from 12 meterological stations for calibration
Simulated maximum increase of annual adult ticks with DD>00C increaseResults
Ontario
Wiarton
▲ Timmins
■ Picton
○ Chatham
2875 DD>00C
Less water surface cooling inlands
Northern locations less likely to be affected by water surface cooling
Fig.2
Objective 2
Theoretical limits for I. scapularis establishment at climate change scenariosResults
Non-cooledNon-cooledCooledCooled
B2 lower
Fig.1
Objective 1
Seasonal tick survival under climate change scenariosResultsFig.3
Objective 3
Larvae
Nymphal
AdultCantham, Ontario
Timmins, OntarioNo current tick population
Established tick population
CGCM2 model
A2 emission
Seasonal tick survival under climate change scenariosResultsFig.3
Objective 3
Larvae
Nymphal
Adult
CGCM2 model
A2 emission
Lower annual mortality
Faster development
More ticks over time
Earlier activity period
Longer activity period
Discussion
Depends on host finding success
Model limitations
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
Disease mostly southern problem (population density)
Thoughts
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
Realistic that I. scapularis populations will establish northwards
Historical correlation (good model)
Conclusions
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!