geographic distribution of blastomycosis in dogs by season northern wisconsin
TRANSCRIPT
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