Fusarium spp. are ubiquitous soil saprophytes and occasional plant pathogens. They are responsible for a variety of superficial and invasive human infectious disease. Fusarium moniliforme, Fusarium oxysporum, and Fusarium solani are the most commonly isolates species. These pathogens produce characteristic fusoid or sickle-shaped macroconidia when cultured on synthetic media, but the tissue forms of these fungi are purely hyphal. Fusoid conidia can also be seen in smears from blood cultures growing these organisms.
The hyphae of the Fusarium spp. are 3 to 8 µm in width, are septate, branched and haphazardly dispersed throughout the lesions. The hyphal branches characteristically arise at right angles from parent hyphae. The hyphae cannot be reliably distinguished from those of Aspergillus spp. Definitive diagnosis requires isolation in culture.
Opportunistic infections frequently begin as cutaneous infections which manifest clinically as painful, erythematous or necrotic nodules that enlarge and ulcerate. The fungi can disseminate to the lungs, kidneys, and other organs.
The image to the right shows Fusarium lactophenol cotton blue slide demonstrating septate filamentous hyphae, and the floral arrangement of the fusiform macroconidia.
Image courtesy of the CDC.