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Blastomyces and Paracoccidioides

Two additional thermally dimorphic fungi are Blastomyces dermatitidis (teleomorph Ajellomyces dermatitidis) [26] and Paracoccidioides brasiliensis [27]. Blastomycosis, endemic in the central US, may remain subclinical, but can also progress to pulmonary and/or extrapulmonary disease with primary involvement ofthe skin, but also bone, prostate, or central nervous system [26]. B. dermatitidis grows in the mycelial phase in soil. Inhalation of conidia from contaminated soil can lead to pulmonary infection and conversion to the pathogenic yeast form.

Paracoccidioiomycosis is one of the most common systemic mycoses in Latin America. Saprobic mycelia of P. brasiliensis in the environment produce conidia which transform to the yeast form after inhalation [27]. The adult form of paracoc-cidioidomycosis occurs predominantly in immunocompetent males. Clinical presentations include primary lung infections, often with resultant fibrosis, and secondary dissemination to skin, lymph nodes, and adrenal glands. The gender bias is probably due to the inhibition of the morphological transition by estrogens [28]. The juvenile form of paracoccidioidomycosis is less frequent (< 10%), but more severe with dissemination to organs of the reticuloendothelial system and increased mortality. Untreated paracoccidioidomycosis is often fatal, current treatment regimens are prolonged, and persistence of the fungus in a dormant state over years is not uncommon.

B. dermatitidis and P. brasiliensis are candidates for future genome sequencing projects at the Broad Institute (http://www.broad.mit.edu/annotation/fungi/fgi/ nominated.html). As a first step towards the genomics of P. brasiliensis an expressed sequence tag (EST) sequencing project has been established, allowing identification of putative virulence genes by homology to genes in other fungi and expression analysis of genes involved in the mycelia-to-yeast transition [29].

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