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