Blastomycosis cannot yet be prevented or controlled, in part because the natural habitat of the causative fungus, Blastomyces dermatitidis, remains ill defined. In investigating 2 outbreaks of blastomycosis that occurred in the summer of 1985 among persons engaged in activities along rivers in contiguous central Wisconsin counties, we isolated B. dermatitidis from soil at one of the riverbanks. Blastomycosis developed in 7 (58%) of 12 residents and guests who had gathered at a pheasant farm on the Tomorrow River in early May, and in 7 (88%) of 8 boys and 1 adult who had visited a site on the Crystal River in early June. Of the 14 patients, 13 (93%) were symptomatic. Two patients visiting the sites only once became ill 23 and 78 days after exposure, respectively. We traced one outbreak to fishing from the bank of the Tomorrow River, and the other to climbing into an underground timber fort along the Crystal River. A culture of soil and organic debris from the fishing site yielded B. dermatitidis. From these and other outbreaks, and studies of endemic disease, we conclude that riverbanks can be a natural habitat of B. dermatitidis, and that the environment around waterways represents the most important site yet identified for transmission of B. dermatitidis.

The first isolation of Penicillium marneffei, obtained from the liver of a rat captured in Viet Nam, was described in 1956. There have been no additional reports of the isolation of this fungus. Recently our laboratory identified this organism in an isolate from the spleen of a patient with Hodgkin's disease. The distinctive features of P. marneffei include the production of the dark red pigment which diffuses into the agar and the ability of this pathogen to exist in dimorphic forms. At 25 C. it develops the structures typical of the genus Penicillium, while at 37 C. the tan, rough colony has a yeast-like consistency, with small, oval or round yeast cells averaging 3 p in diameter mixed with short, hyphal elements. Histologically, the organism may resemble Histoplasm capsulatum.

The inhalation of conidia of Blastomyces dermatitidis, a fungus found in soil, causes disease in humans and animals. We studied the genetic diversity of this pathogen by extracting DNA yeasts and analyzing them with a polymerase chain reaction (PCR)-based typing system we developed, which used restriction fragment analysis of amplicons from the regions between the rDNA repeats and allowed us to class isolates into 3 major groups. Strains were further 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 contained 17, 23, and 19 isolates, which were divided into 5, 15, and 12 types, respectively. All 16 isolates from North America in group A were from the upper midwestern United States or Canada, whereas 0 of 20 isolates from the southeastern United States were in group A. Studies of the largest collection from 1 locale (Eagle River, WI), revealed that the soil isolates studied were not responsible for the majority of cases in this outbreak, as previously proposed, and that >1 strain was present in the environment and in patients. Overall, these results provide a tool for the epidemiological study of blastomycosis and illuminate the genetic and geographic diversity of this important pathogen.

No abstract

No abstract