1. All four species are probably mainly saprotrophic in the soil, having become serious pathogens mainly because of their ability to grow at 37C, evade the human immune system, bind to human tissue, and produce proteases.
Pathogenicity is probably coincidental and represents a dead end in the life cycle of these fungi because the transmission of inoculum from infected humans to the environment or to other humans is negligible.
Infection of humans occurs by inhalation of microconidia produced in the soil. These are sufficiently small to penetrate into the alveoli of the lung. There, yeast-like stages are formed which are the agents of disease. This is in contrast to Candida albicans where hyphae rather than yeast cells represent the invasive stage.