Geographic Distribution of
Blastomycosis in Dogs by Season
Northern Wisconsin
1,2,4
Baumgardner ,
Dennis J.
3
Daniel P. Paretsky , Zachary
Baeseman4, Andrea Schreiber1
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•
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1. Center for Urban Population Health
2. Aurora UW Medical Group
3. Eagle River Animal Hospital
4. University of Wisconsin School of
Medicine and Public Health
Blastomycosis
• A potentially fatal systemic and cutaneous fungal
infection
• Etiology: Blastomyces dermatitidis
• Infection follows inhalation of spores
• Ecological niche incompletely defined
• Difficult to isolate from soil
• High % asymptomatic disease
• No reliable skin test
Seasonality of Blastomycosis
• Previous studies: conflicting results:
– No conclusive seasonality, including in humans
in Northern Wisconsin (WREN 2007)
• Seasonality might suggest certain
environmental factors, or
• Environmental factors may differ by season
Coccidioides
• Climate accounts for much variability in
southern Arizona
• Increased antecedent precipitation, then
increased temperatures and drought,
followed by wind or excavation dust
dispersal leads to infection (the “grow and
blow” hypothesis).
Why is a people doctor studying
dogs?
• Environmentally acquired infection
• Dogs “harbinger” – same geographic
distribution as humans
• 10 – 14 dog cases for every human
• Dogs may be less restricted geographically
than humans
Methods
• Demographic data and street addresses from
registries geocoded with Map Marker Plus,
mapped with Arc-GIS
• CrimeStat III for spatial modeling
• Season/month of diagnosis
• Weather data from local weather station
• Data control charts generated for seasonal
data
Dog Study 1990-2008
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Single veterinarian practice, Eagle River
A highly endemic area
219 resident dogs in catchment area
202 dogs in Vilas County
• Controls were 200 randomly selected Vilas
addresses from 2001 practice registry
Statistical analysis
• Chi-squared test for categorical data
• Mood’s median test performed on the
geographic distribution data
• An individual/moving range control chart
was constructed, by season, for dog cases
1990-2008
• Stepwise regression for weather data
Results
I and MR Chart for Dog Cases
Individual Value
10
5
Mean=3.014
0
LCL=-3.317
Subgroup
YR
Moving Range
UCL=9.344
8
7
6
5
4
3
2
1
0
0
10
20
30
40
50
60
70
1992
1995
1997
2000
2002
2005
2007
UCL=7.777
R=2.380
LCL=0
Dogs by Season p=0.06
80
70
60
50
40
30
20
10
0
Win
Spring
Sum
Fall
Dogs by Season
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•
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•
Winter 24%
Spring 18%
Summer 36%
Fall 22%
• Summer vs. other
months:
– P=0.02
• May be differential
outdoor exposure vs.
humans
– Dogs sniff/dig
• Or real differences
– Weather?
Dog median distance to nearest
waterway, m.
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•
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Winter
Spring
Summer
Fall
155 m.
204 m.
137 m.
183 m.
• All 4: p=0.09
• Summer vs. other
seasons: p=0.08
• Summer vs. Spring:
p=0.02
Dog Cases Warm (Apr-Sept:125)
vs. Cold (Oct-March:89) Months
140
120
100
80
# of Cases
60
40
20
0
Warm
Cold
Seasonal Weather Data
Best 4 season model:
– Inverse relationship with Max. Temp 2 seasons
prior and direct relationships with Mean Max.
Temp 2 seasons prior, and Mean Ave. Temp
and Total Precipitation 4 seasons prior
(explains 32% of variation) [p=0.000]
Seasonal Weather Data
Best model: uses warm (AprilSeptember)/cold 6 month time periods
– Direct relationships with total precipitation 2
periods prior and mean maximum temperature
1 period prior, and inverse relationship with
mean average temperature 1 period prior
(explains 67% of variation) [p=0.000]
Regression Equation
• # of New cases = 0.967 (mean maximum
Temp., one 6 month block prior) – 0.907 (
mean average Temp., one block prior) +
0.554 (total precipitation in the 6 month
block , 2 blocks prior) – 13.7
• Maybe a “grow and tolerate change” model
Conclusions
• The geographic distribution of cases of
blastomycosis in dogs in Northern Wisconsin has
remained constant over time and season
• This suggests that some relatively fixed
environmental factors are important in the ecology
of the etiologic fungus
• Further studies are needed regarding the effects of
precipitation and temperature
Acknowledgements
• Supported, in part, by a donation to the St.
Luke’s Foundation by Mr. & Mrs. Charles
Goldsworthy, Eagle River, WI
• The dogs and owners represented here