No abstract

Geographic information systems (GIS) are powerful tools for investigating the ecogeography of environmentally acquired infections. GIS technology was used to geocode and map cases of blastomycosis, by household, of human and dog residents of Vilas County, Wisconsin, USA. Human case households (n = 136) were from a comprehensive street address registry 1979--2001; human controls were 200 random-number selected households from 2001 county tax records. Dog cases (n = 116) were from a consecutive street address registry from a private veterinarian practice, Eagle River; dog controls were 200 random-number selected addresses from the 2001 total practice registry. Where geocoding was not available from existing maps, home sites were visited and geocoded using a handheld global positioning system (n = 61). Waterway characteristics were obtained from the Wisconsin Department of Natural Resources GNIS database, soil type data from the USDA. Data were analysed with chi-square and Mann-Whitney tests; cluster analysis with CrimeStat II software. A disproportionate number of human and dog cases were associated with waterways of the western Eagle River area. Human and dog cases were more commonly near waterways < 500 m elevation (more nutrient rich) (P < or =0.001 for both) and were associated with sands (prone to drought) (P < or = 0.01 for both). When the nearest waterway was a lake, case addresses were more commonly near lakes with <7.6 m maximum depth (more lake mixing) (P <0.05, humans and dogs) but mean depth, type and size of lakes did not differ from controls. Further studies are needed to clarify the nature of these associations.

Dogs and humans acquire Blastomyces dermatitidis infections from the same incompletely defined habitat. Studies of blastomycosis cases have not consistently demonstrated seasonality or significant antecedent climate effects. To determine the distribution of disease by season, we studied over 18 years 219 dogs with blastomycosis from a single veterinary practice in Northern Wisconsin. The 202 Vilas County dog addresses were compared to 200 random-number selected addresses from the practice registry. Street addresses were geocoded and mapped using ArcGIS, including ratio of cases/random addresses to construct a control chart. Stepwise and linear regression was used to model case counts by season and by 6 month warm (April-September) and cold periods, using lagged local weather data. The geographic distribution of cases was found to be similar regardless of season and time period, and no season exceeded control chart limits. Seasonal distribution of cases was; winter (n = 53, 24%), spring (39, 18%), summer (79, 36%), fall (48, 22%), p = 0.002. When cases were considered by 6-month warm/cold periods, 67% of variation is explained by the total precipitation which occurred two periods prior, and lower average temperature, but higher maximum temperature one period prior (p = 0.000). Weather parameters along with fixed and variable environmental factors likely determine the occurrence of B. dermatitidis, perhaps as part of a 'grow and tolerate change' model.

Environmental isolations of the dimorphic fungus, Blastomyces dermatitidis, the aetiologic agent of blastomycosis are rare, and have usually involved animal innoculation techniques. We report the in vitro isolation of B. dermatitidis from a woodpile in November 1997, from a private property in a highly endemic area of north central Wisconsin, USA. The woodpile was 73 m from the Wisconsin River and 5 m from a kennel which had housed nine dogs over the past 14 years, four of which had been diagnozed with blastomycosis. One of 19 samples from the property yielded B. dermatitidis after 37 °C incubation in a neutral aqueous solution of allantoin, Tween‐80, potassium phosphate, magnesium sulphate, penicillin and streptomycin followed by plating on yeast‐extract phosphate agar at 20 °C. Refinements of this technique may help further elucidate the ecological niche of B.dermatitidis.

Environmental isolations of the dimorphic fungus, Blastomyces dermatitidis, the aetiologic agent of blastomycosis are rare, and have usually involved animal inoculation techniques. We report the in vitro isolation of B. dermatitidis from a woodpile in November 1997, from a private property in a highly endemic area of north central Wisconsin, USA. The woodpile was 73 m from the Wisconsin River and 5 m from a kennel which had housed nine dogs over the past 14 years, four of which had been diagnosed with blastomycosis. One of 19 samples from the property yielded B. dermatitidis after 37 degrees C incubation in a neutral aqueous solution of allantoin, Tween-80, potassium phosphate, magnesium sulphate, penicillin and streptomycin followed by plating on yeast-extract phosphate agar at 20 degrees C. Refinements of this technique may help further elucidate the ecological niche of B. dermatitidis.