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Geographic Distribution of Blastomycosis in Dogs by
Season
Northern Wisconsin
Dennis J. Baumgardner1,2,4, Daniel P. Paretsky3, Zachary
Baeseman4, Andrea Schreiber1
• 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
• 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
0Subgroup 10 20 30 40 50 60 70
0
5
10
Indiv
idual V
alu
e
1992 1995 1997 2000 2002 2005 2007YR
Mean=3.014
UCL=9.344
LCL=-3.317
012345678
Movi
ng R
ange
R=2.380
UCL=7.777
LCL=0
I and MR Chart for Dog Cases
Dogs by Season p=0.06
0
10
20
30
40
50
60
70
80
Win Spring Sum Fall
Dogs by Season
• 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.
• Winter 155 m.• Spring 204 m.• Summer 137 m.• Fall 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
0
20
40
60
80
100
120
140
Warm Cold
# of Cases
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 (April-September)/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
15
10
5
0
20051998Date/Time
Regression Model: Dogs Warm vs. Cool months '90-08
Circle=Predicted; Plus=Actual
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