Asexual reproduction manifests in one of two forms: the Scedosporium type (the most common type) and the Graphium type. Scedosporium apiospermum forms greyish-white colonies with a grey-black reverse. The conidia are single-celled, pale brown and oval in form. Their size ranges from 4–9 x 6–10 μm and their development is annellidic. Pathogenicity
Pseudallescheria boydii is an emerging opportunistic pathogen. Immune response is characterized by TLR2 recognition of P. boydii derived α-glucans, while TLR4 mediates the recognition of P. boydii derived rhamnomannans. Human infection takes one of two forms: mycetoma (99% of infections), a chronic, subcutaneous disease, and pseudallescheriasis, which includes all other forms of the disease commonly presented in the central nervous system, lungs, joints and bone. The former can also be distinguished by the presence of sclerotia, or granules, which are typically absent in pseudallescheriasis-type infections. Infection is initiated via inhalation or traumatic implantation in the skin. Infection can lead to arthritis, otitis, endocarditis, sinusitis, and other manifestations. Masses of hyphae can form "fungus balls" in the lungs. While "fungus balls" can also form in other organs, they are commonly derived from host necrotic tissue resulting from nodular infarction and thrombosis of lung vessels following infection.This species is second in prevalence after Aspergillus fumigatus as a fungal pathogen in cystic fibrosis patients. It causes allergic bronchopulmonary disease and chronic lung lesions that resemble aspergillosis. Infections can also occur in immunocompetent individuals, usually in the lungs and upper respiratory tract.
Furthermore, P. boydii grains and hyphae should be cultured and observed microscopically after staining with H&E, periodic acid–Schiff stain, Tissue Gram or Grocotts methenamine silver stain. A radiological diagnosis may be helpful in elucidating the extent of the disease in terms of bone and soft tissue involvement. Scedosporium-caused eumycetomas have been found to have thick-walled cavities and grains appearing as hyperreflective echoes on scans, while actinomycetomas show fine echoes at the bottom of cavities.Direct detection is possible in samples histochemically stained in 20% KOH followed by fluorescence microscopy with antibody. The characteristic shape, texture and colour of tissues can help identify S. apiospermum grains, which are often surrounded by an eosinophilic zone. Histopathologically, hyalohyphomycotic fungi like Scedosporium spp., Aspergillus spp., Fusarium spp. and Petriella spp. are similar in that they show septation of hyphae at regular intervals, have dichotomous branching and invade blood vessels. However, Scedosporium presents more irregular branching, sometimes with terminal or intercalary chlamydospores. In serum, Scedosporium infections can be detected by counterimmunoelectrophoresis. Molecular diagnostics appear to be promising in complementing current conventional diagnostic methods.Culture detection is accomplished by rinsing "grains" in 70% ethanol and sterile saline solution to avoid bacterial contamination prior to inoculation on growth medium. Selection of Scedosporium growth can be achieved on Leonians agar supplemented with 10 g/mL benomyl, or on media containing cycloheximide or amphotericin B. Optimal incubation is at a temperature of 25–35 °C (77–95 °F). Treatment
Pseudallescheria boydii is resistant to amphotericin B and nearly all other antifungal drugs.