P. brasiliensis is the thermally dimorphic fungal agent of paracoccidioidomycosis (South American blastomycosis), which is confined to endemic regions of Central and South America.
Morphology and Identification
Cultures of the mold form of P. brasiliensis grow very slowly and produce chlamydospores and conidia. The features are not distinctive. At 36°C, on rich medium, it forms large, multiply budding yeast cells (up to 30 µm). The yeasts are larger and have thinner walls than those of B. dermatitidis. The buds are attached by a narrow connection (Figure 1).
Fig1. Paracoccidioidomycosis. Large, multiply budding yeast cells (15–30 µm) are observed in cutaneous lesion. KOH 400×.
Pathogenesis and Clinical Findings
P. brasiliensis is inhaled, and initial lesions occur in the lung. After a period of dormancy that may last for decades, the pulmonary granulomas may become active, leading to chronic, progressive pulmonary disease or dissemination. Most patients are 30–60 years of age, and over 90% are men. A few patients ( <10%) , typically less than 30 years of age, develop an acute or subacute progressive infection with a shorter incubation time. In the usual case of chronic paracoccidioidomycosis, the yeasts spread from the lung to other organs, particularly the skin and mucocutaneous tissue, lymph nodes, spleen, liver, adrenals, and other sites. Many patients present with painful sores involving the oral mucosa. Histology usually reveals either granulomas with central caseation or microabscesses. The yeasts are frequently observed in giant cells or directly in exudate from mucocutaneous lesions.
Skin test surveys have been conducted using an antigen extract, paracoccidioidin, which may cross-react with coccidioidin or histoplasmin.
Diagnostic Laboratory Tests
In sputum, exudates, biopsies, or other material from lesions, the yeasts are often apparent on direct microscopic examination with KOH or calcofluor white. Cultures on Sabouraud’s or yeast extract agar are incubated at room temperature and confirmed by conversion to the yeast form by in vitro growth at 36°C. Serologic testing is most useful for diagnosis. Antibodies to paracoccidioidin can be measured by the CF or ID test. Healthy persons in endemic areas do not have antibodies to P. brasiliensis. In patients, titers tend to correlate with the severity of disease.
Treatment
Itraconazole appears to be most effective against paracoccidioidomycosis, but ketoconazole and trimethoprim sulfamethoxazole are also efficacious. Severe disease can be treated with amphotericin B.
Epidemiology
Paracoccidioidomycosis occurs mainly in rural areas of Latin America, particularly among farmers. The disease manifestations are much more frequently in males than in females, but infection and skin test reactivity occur equally in both sexes. Since P. brasiliensis has only rarely been isolated from nature, its natural habitat has not been definitively determined. As with the other endemic mycoses, paracoccidioidomycosis is not communicable.
