Susceptibility to aspergillosis is greatly increased in the immunocompromised and malnourished avian patient. Stress pre-existing disease, and the prolonged use of antibiotics and steroids, may further increase a bird's susceptibility. Contaminated food, water, and nesting material are sources of exposure to spores. In birds, aspergillosis is primarily a disease of the lower respiratory tract. Although the lungs and air sacs are usually involved, the trachea, syrinx, and bronchi may be affected as well.
Infection can spread from the respiratory tract to pneumatized bone or enter the peritoneal cavity.
Any organ can become infected by the fungus. In the acute form, anorexia, dyspnea, or sudden death may occur. White, mucoid exudation, marked congestion of the lungs and air sacs, and pneumonic nodules may be present. In the chronic form, dyspnea, voice change, lethargy, depression, emaciation, polydipsia, and polyuria may occur. Extensive involvement of the respiratory tract can be present before clinical signs are apparent.