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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!