Paracoccidioides

Paracoccidioides is a genus of thermally dimorphic fungi that causes paracoccidioidomycosis, a systemic mycosis of Latin America. The species most commonly implicated in human disease are Paracoccidioides brasiliensis and Paracoccidioides lutzii, together forming a species complex with distinct antigenic profiles.

In the environment, Paracoccidioides exists as mold with conidia; in the human host at body temperature it converts to a yeast form. The yeast displays characteristic multiple budding around a central cell, often described as a pilot wheel. The fungus is typically acquired by inhalation of fungal propagules from soil or plant material, particularly in rural and agricultural settings. Men are more frequently affected, in part because estrogens in females inhibit the mold-to-yeast transition, reducing susceptibility.

Clinical presentation varies by age. Acute or subacute forms occur in children and young adults and may involve lymphadenopathy, skin lesions, and disseminated disease. The chronic form is more common in adults and predominantly affects the lungs, but can also involve mucocutaneous sites, bones, and lymphatics. Immunocompromised individuals are at risk for more severe disease.

Diagnosis relies on direct demonstration of yeast or mold in clinical specimens, culture, and histopathology showing the characteristic yeast with multiple buds. Serology (immunodiffusion, complement fixation) supports diagnosis, though performance can differ between species; molecular methods are increasingly used. Serologic tests may be less sensitive for Paracoccidioides lutzii due to antigen differences.

Treatment consists of long courses of antifungals. Itraconazole is a first-line option for mild-to-moderate disease; amphotericin B is used for severe cases, followed by consolidation therapy. Trimethoprim-sulfamethoxazole is an alternative. With appropriate therapy, prognosis is generally favorable, though relapse can occur.