1. L I T E R A T U R E R E V I E W
M A T T H E W W E I K
G E O G 5 2 5
M A Y 4 T H , 2 0 1 5
The Influence of Forest
Fragmentation on Lyme Disease
in the Upper Midwest

2. Outline
 Introduction
 Background
 Geography of Lyme disease
 Transmission Cycle
 Land Use and Geographic Expansion
 Lyme disease and GIS Data
 Conclusion

3. Introduction
 Arthropod borne
 Reproduced within ticks
 Has highest prevalence in the U.S.
 CDC reports 30,831 cases in 2012

4. Background
 Zoonotic pathogen
 Zoonosis: transfer of disease from host to host using a vector.
 Majority of emerging diseases
 Endemic Areas
 CDC: Counties with at least two locally acquired cases
 Or having a tick vector tested positive for the pathogen

5. Geography of Lyme disease
 Historic
 Present for thousands of years
 Spread from Northeast to West
 Declined with deer and tick populations (500-110 years ago)
 Currently
 Cases Within Major Clusters:
 Northeast - 80%
 Upper Midwest - 11%
 Pacific West - 9%
 Major Cluster Increasing in LDI
 Ixodes scapularis (vector) is spreading range within clusters
 Borrelia burgdorferi (pathogen) infection follows

6. Geography of Lyme disease
 Geographic Expansion
 Rarely studied and understood outside endemic regions
 May rely on different tick vectors
 I. pacificus in Pacific Coast, and dual transmission cycle
 I. affinis and I. major (exclusively rodent feeding) in North Carolina plain
 I. scapluaris range expansion
 Reforestation, suburbanization, reintroduction of deer populations
 Variation within range results from climate, habitat suitability, and growing season
 Texas and Mexico
 I. scapularis and hosts infected with pathogen have been found
 Canada
 Southeast region is becoming an endemic region
 Climate change and location near Major endemic regions

7. Transmission Cycle
 Establish Disease Reservoir
 Nymph I. scapularis obtains infection
 During larval blood meal
 Infection spreads to new hosts
 During nymph blood meal
 Becomes adult and reproduces
 During following autumn
 Human Infection
 Uninfected larvae feed on infected hosts
 Mid-summer
 Larvae acquire infection
 molt into nymph
 Transfers infection to humans during next feeding
 Nymphs are most likely to spread disease
 Adults are active at different time of year
 More selective of host
 Longer time for transfer of pathogen to host (24+ hours)

8. Land Use and Expansion
 Land use pattern influence on Lyme disease
 Observed for similar tick-borne pathogens
 Provide ideal habitats for primary hosts of the transmission cycle
 Speed of human modification increases magnitude of impact
 Urban land use
 High LDI where Low density residential built into forests.
 Agriculture land use
 Limits locations of suitable habitat for I. scapularis within range
 Forest Fragments
 Division of contiguous forests
 Increases distance between patches
 Increases the ratio between forest edge and interior
 Decreases Biodiversity and allows cycle to thrive
 Lack of competitors or predators
 Mice populations reach high densities
 Decreased host composition increases feedings on highly competent reservoir hosts

9. Lyme disease and GIS Data
 Lyme disease Data:
 CDC provides number of cases of Lyme disease by county, and incidence by state
 Cases by county:
 1992-2011, five year intervals
 Includes 2012 and 2013 as well
 Process:
 State/local health departments gather data
 National Notifiable Diseases Surveillance System (NNDSS) removes personal
identifiers
 NNDSS communicates with the CDC
 Geographic Limitations:
 Possible under reporting where not recognized
 Over reporting in endemic regions
 Human movement displaces people from true origin of disease

10. Lyme disease and GIS Data
 Land Use/ Land Cover
 Downloaded from USGS GAP analysis program
 Traditionally used to for prediction of protected species within conservation
areas
 USGS provides additional projects in GAP Application Index
 Very specific detail
 590 total land use classes
 General categories create eight classes
 Detailed vegetation and land use patterns for contiguous U.S.
 Created using satellite imagery
 Landsat TM satellite Imagery from 1999 to 2001
 30m X 30m pixel
 Minimum mapping unit: 0.4 ha or 1 acre
 Overlooks small patches of vegetation in modeling process.

11. Lyme disease and GIS Data
 Lyme disease modeling
 Risk models created east of 100th parallel
 Typically based on DON, NIP, and DIN
 DIN is specific entomological indicator of risk
 Traditional models based on tick data collected in 1998
 Forest fragment and Lyme disease modeling
 Fragments have been defined between 0.7 and 7.6 hectares
 Smallest fragments resulted in 3x increases in DON
 DIN was increased 7x in fragments less than 1.2 hectares

12. Conclusion
 Lyme disease is most reported arthropod borne disease in U.S.
 Geographically clustered in Northeast, Upper Midwest, and Pacific
Coast, but is spreading south and north as well
 Human infection is the result of a natural transmission cycle
 Land use patterns of urban, agriculture, and forest
 fragmentation influence the risk of Lyme disease where endemic
 Data for both Lyme disease and Land use can be downloaded and
used for modeling of disease risk

13. Question?