Aspergillus fumigatus is an ubiquitous, saprophytic fungi which is the primary causative agent of Aspergillosis. A. fumigatus is commonly found growing on dead or decaying matter in the environment. Frequent growth sources include soil, decaying vegetables,ensilage, bedding (hay, straw, wood shavings, saw dust, etc.), and moldy feed. A. fumigatus growth increases in warm, humid weather conditions.
A. fumigatus produce conidia (asexual spores) which are easily dispersed into the air, ensuring ubiquity in both indoor and outdoor environments. The primary route of infection in poultry is via inhalation of these airborne conidia, followed by conidial deposition in the lung, air sacs, or trachea. Usually, in healthy birds, the mucosal defenses of their respiratory system aid in removal of the conidia without resulting in disease. However, in birds with a compromised immune system, their mucosal defenses aren't able to work properly, leading to fungal colonization and growth.