1. Geographic Distribution of Blastomycosis in Dogs by Season
Northern Wisconsin

2. Dennis J. Baumgardner1,2,4, Daniel P
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

3. 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

4. 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

5. 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).

6. 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

7. 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

8. 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

9. 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
Stepwise regression for weather data

11. Results

14. Dogs by Season p=0.06

15. 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?

17. Dog median distance to nearest waterway, m.
Winter m.
Spring m.
Summer 137 m.
Fall m.
All 4: p=0.09
Summer vs. other seasons: p=0.08
Summer vs. Spring: p=0.02

18. Dog Cases Warm (Apr-Sept:125) vs. Cold (Oct-March:89) Months

19. 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]

20. 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]

21. Regression Equation
# of New cases = (mean maximum Temp., one 6 month block prior) – ( mean average Temp., one block prior) (total precipitation in the 6 month block , 2 blocks prior) – 13.7
Maybe a “grow and tolerate change” model

23. 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

24. 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