zoonoses and communicable diseases common to ... - PAHO/WHO

BLASTOMYCOSIS 311BLASTOMYCOSISICD-10 B40.0 acute pulmonary blastomycosis; B40.1 chronic pulmonaryblastomycosis; B40.3 cutaneous blastomycosis; B40.7 disseminatedblastomycosis; B40.8 other forms of blastomycosisSynonyms: North American blastomycosis, Chicago disease, Gilchrist’s disease.Etiology: Blastomyces dermatitidis,a dimorphic fungus existing in mycelial formin cultures and as a budding yeast in the tissues of infected mammals. The fungusalso exists as yeast in enriched culture media at 37°C. The mycelial form in culturemedia at 25°C is cottony white, turning to brown over time.Sandy, acidic soil close to rivers or other freshwater reservoirs is the microecosystemmost favorable to B. dermatitidis. It remains in an infective sporulatedstate in this biotope, as its spores (conidia) can detach and become airborne. Highambient humidity seems to favor the release of spores.B. dermatitidis is subdivided into two serotypes (1 and 2) based on the presenceof an exoantigen, called A and recognized by a specific precipitin. Strains examinedfrom India, Israel, and the United States, and one strain examined from Africa allcontained A antigen (serotype 1). Eleven of 12 African strains examined were type2. The African strains are deficient in A antigen, but contain K antigen (Kaufman etal., 1983).Geographic Distribution: The disease has been observed in eastern Canada,India, Israel, South Africa, Tanzania, Tunisia, Uganda, the United States, andthe former Zaire. Autochthonous cases have also occurred in some Central andSouth American countries (Klein et al., 1986). In the United States, endemic areasare located along the Mississippi, Missouri, and Ohio rivers, and in parts of NewYork State. In Canada, they are located along the St. Lawrence River and near theGreat Lakes.Occurrence in Man: Predominantly sporadic. Most of the cases have beenrecorded in the United States, with the highest prevalence in the Mississippi andOhio river basins. From 1885 to 1968, there were 1,573 cases in that country(Menges as cited by Selby, 1975). Klein et al. (1986) summarized from the literaturethe incidence in different endemic U.S. states: from 0.1 to 0.7 cases per 100,000inhabitants per year in Arkansas from 1960 to 1965; 0.61, 0.44, and 0.43 cases per100,000 inhabitants per year in Mississippi, Kentucky, and Arkansas, respectively,from 1960 to 1967; and 0.48 cases per 100,000 inhabitants per year in Wisconsinfrom 1873 to 1982. Hyperendemic areas in these states have an incidence of 4 casesper 100,000 per year. These data do not include slight cases of the disease that donot generally receive medical attention.In Louisiana (USA), an attempt was made to identify all cases that occur in thestate and to study one district in detail (Washington Parish) that is consideredendemic. The average annual incidence for the entire state during 1976–1985 was0.23 cases per 100,000 inhabitants, while the incidence for Washington Parish was6.8 cases per 100,000. In 30 cases studied in this district, the patients’ ages rangedfrom 3 weeks to 81 years. Five people died, and one of these was probably infectedin utero (Lowry et al., 1989).