Etiology of Pulmonary Aspergillosis
Aspergillus widely exists in the natural world, accounting for about 12% of all the fungi in the air. It is provided by dead plants, animal feces, and dead bodies of animals and is a saprophytic fungus parasitizing in the soil. Aspergillus is a general term for filamentous fungi with resembling properties which is categorized into the genus Aspergillus. Its nutrient hypha has septum, and part of the hypha grows into long and coarse conidiophore with apical flask-shaped or sphere-shaped vesicle and surface sterigmata. The sterigmata are commonly two-layer structure, with strands of spherical conidia of coarse surfaces attached. The conidiophore, apical vesicle, sterigmata, and conidium constitute spore head (Fig. 2.1). There are at least 170 kinds of Aspergillus within human knowledge. The conidium may be yellow, green, black, brown, or orange, and the color is the basis for identification of its strain. The conidiophore grows on the Sertoli cell and connects to the nutrient hypha via the Sertoli cell. The morphology of aspergillus spore panicle includes the length of conidiophores, shape of the apical vesicle, and single or double small peduncle. The shape, size, surface structure, and color of the conidium are the basis for identification of its strain. The most optimal temperature for the growth of aspergillus is 25–30 °C. The most common pathogenic aspergillus is Aspergillus fumigatus , followed by Aspergillus flavus and Aspergillus niger. Other rarely found aspergilla include Aspergillus candidus, Aspergillus glaucus , Aspergillus parasiticus , Aspergillus terreus , Aspergillus versicolor , and Aspergillus oryzae.