Pseudallescheria

Pseudallescheria is a genus of fungi in the phylum Ascomycota. It represents the sexual (teleomorphic) state of certain fungi whose environmental and clinical forms are commonly classified in the genus Scedosporium. Environmental species of Pseudallescheria are widely distributed in soil and polluted water and can be found in association with human-made environments.

Taxonomy and species. The best-known member is Pseudallescheria boydii, historically linked with human infections and commonly associated with the anamorph Scedosporium apiospermum. Other described species have been reported, and the relationship between Pseudallescheria and Scedosporium illustrates teleomorph–anamorph nomenclature in fungi.

Clinical significance. Pseudallescheria/Scedosporium species are opportunistic pathogens capable of causing pulmonary, sinus, subcutaneous, and central nervous system infections, as well as eumycetoma, particularly in immunocompromised hosts. Infections may follow traumatic implantation or inhalation and can occur after near-drowning exposure due to contaminated water. Infections caused by Pseudallescheria boydii can be resistant to some antifungals, and clinical outcomes depend on host status and the extent of disease.

Diagnosis and treatment. Diagnosis relies on culture, microscopy, histopathology, and molecular methods to identify the sexual state, with clinical laboratories often noting the associated Scedosporium species. Treatment is challenging because antifungal susceptibility is variable; voriconazole is frequently effective, whereas resistance to amphotericin B is common. Management may require prolonged antifungal therapy and surgical debridement for localized lesions.

Taxonomic notes. Modern taxonomy often emphasizes the one-name system, but traditional literature distinguishes the teleomorph Pseudallescheria from the anamorph Scedosporium, reflecting historical classification practices in mycology.