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Geographic Distribution of Blastomycosis in Dogs by Season Northern Wisconsin.

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Presentation on theme: "Geographic Distribution of Blastomycosis in Dogs by Season Northern Wisconsin."— Presentation transcript:

1 Geographic Distribution of Blastomycosis in Dogs by Season Northern Wisconsin

2 Dennis J. Baumgardner 1,2,4, Daniel P. Paretsky 3, Zachary Baeseman 4, Andrea Schreiber 1 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 Moods 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

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11 Results

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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?

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17 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

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 = 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

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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. Lukes Foundation by Mr. & Mrs. Charles Goldsworthy, Eagle River, WI The dogs and owners represented here

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