Molecular epidemiology of Blastomyces dermatitidis

The inhalation of conidia of Blastomyces dermatitidis, a fungus found in so il, causes disease in humans and animals. We studied the genetic diversity of this pathogen by extracting DNA yeasts and analyzing them with a polymer ase chain reaction (PCR)-based typing system we developed, which used restr iction fragment analysis of amplicons from the regions between the rDNA rep eats and allowed us to class isolates into 3 major groups. Strains were fur ther differentiated by use of PCR fingerprinting with 3 different primers. Fifty-nine isolates collected over 35 years from 15 regions (United States, India, Africa, Canada) were analyzed. Genotypic groups A, B, and C contain ed 17, 23, and 19 isolates, which were divided into 5, 15, and 12 types, re spectively, All 16 isolates from North America in group A were from the upp er midwestern United States or Canada, whereas 0 of 20 isolates from the so utheastern United States were in group A. Studies of the largest collection from 1 locale (Eagle River, WI), revealed that the soil isolates studied w ere not responsible for the majority of cases in this outbreak, as previous ly proposed, and that >1 strain was present in the environment and in patie nts, Overall, these results provide a tool for the epidemiological study of blastomycosis and illuminate the genetic and geographic diversity of this important pathogen.