Fusarium and Other Opportunistic Hyaline Fungi

This chapter focuses on those fungi that grow in tissue in the form of hyaline or lightly colored septate hyphae. These fungi include Fusarium and other hyaline fungi. Disease caused by hyaline fungi is referred to as hyalohyphomycosis. Hyaline fungi described in this chapter include the anamorphic, asexual hyphomycetes and coelomycetes, as well as homothallic ascomycetes that produce sexual structures and ascospores in culture. Phenotypic/morphologic identification of hyaline moulds is based on methods of conidiogenesis and spore formation; however, accurate species-level identification frequently requires DNA sequence data from one or more informative loci. Molecular phylogenetic analysis has revealed that several Fusarium morphospecies actually represent species-rich species complexes, including the following six species complexes: F. solani, F. oxysporum, F. fujikuroi, F. incarnatum-F. equiseti, F. chlamydosporum, and F. dimerum. Fusarium species are cosmopolitan soil saprobes that can cause toxicosis or infection in humans. A frequent infection in immunocompetent humans is keratitis resulting from trauma or contamination of contact lenses/solutions. Severe disseminated fusarial infections are seen in patients with hematological malignancy or an allogenic hematopoietic stem cell transplant. The portal of entry is unknown in most cases of invasive fusarial infections; however, inhalation of airborne conidia appears to be the most common mode of transmission. Other hyaline fungi can cause human infection as well, ranging from cutaneous to disseminated systemic invasive infections. In general, the recovery of a hyaline fungus from a normally sterile site and microscopic evidence of tissue damage provide the most convincing evidence of invasive disease.