ABSTRACT
Aspergillus is a ubiquitous soil-dwelling organism found in organic debris, dust, compost, foods, spices, and rotted plants. The genus Aspergillus includes over 185 species. Around 20 species have so far been reported as causative agents of opportunistic infections in humans. Among these, Aspergillus fumigatus is the most commonly isolated species, followed by Aspergillus flavus and Aspergillus niger. Aspergillus oryzae, Aspergillus terreus, Aspergillus ustus, and Aspergillus versicolor are among the other species less commonly isolated as opportunistic pathogens (Rinaldi, 1983). Aspergillus spp. are well known to play a role in three different clinical settings in humans: (1) opportunistic infections, (2) allergic states, and (3) toxicoses. Immunosuppression is the major factor predisposing to development of opportunistic infections (Ho and Yuen, 2000). Aspergillus, like other lamentous fungi, is primarily acquired from an inanimate reservoir, usually by the inhalation of airborne spores. The organism grows best at 37°C, and the small spores (2-3 µm) are easily inhaled and deposited deep in the lungs, leading to a variety of clinical syndromes (Figure 14.1). These infections may present in a wide spectrum, varying from local involvement to dissemination and as a whole called aspergillosis. Among all lamentous fungi, Aspergillus is in general the most commonly isolated one in invasive infections. It is the second most commonly recovered fungus in opportunistic mycoses following Candida. Although these are distinct pulmonary entities, on rare occasions, one condition may change to another; for example, an aspergilloma may change to invasive pulmonary aspergillosis (IPA) (Tomee et al., 1995).
