Aspergillus fumigatus: Saprotroph to pathogen

Abstract

Most moulds propagate and disseminate via release of airborne spores, but none surpass the capacity of Aspergillus fumigatus to cause human disease. A. fumigatus is a filamentous fungus that is capable of saprophytic growth in the natural environment and parasitic growth in susceptible human and animal hosts. How does the transition from saprophytic soil-dweller to life-threatening pathogen come about? As the quest for A. fumigatus virulence factors continues apace, our understanding of the pathogenic qualities expressed by this "accidental pathogen” has reached a new, higher order appreciation of the host-pathogen interaction and how this fragile interrelationship might be tipped towards or against initiation or resolution of disease. A. fumigatus has the ability, more than any other airborne fungal pathogen, to radically alter the trade-off between parasitic growth rate and host response in favour of fungal dominance. In this chapter, we will examine the pivotal processes occurring after spore inhalation and incorporate them into a three-step cause-and-effect framework, comprising a comprehensive overview of the host and pathogen factors that drive disease.