ASK THE VET (Aspergillosis/Part I)

Aspergillosis is the most frequently occurring fungal infection in birds. It occurs in acute and chronic forms. The acute form primarily occurs in young birds and newly imported birds and is the result of exposure to a large number of spores. The chronic form is more likely to occur in older birds that have been in captivity. Aspergillosis spores are widespread in the environment and many birds may carry them in their lungs and air sacks until immunosuppression or stress triggers clinical disease. Aspergillosis has been diagnosed in a variety of captive and free-living species of birds. It is characteristically a disease of captivity and close confinement, particularly when birds are kept in an unclean environment. Aspergillosis is most commonly caused by A. fumigatus, although A. flavus, A. niger, A. nidulans, and A. terreus may cause the disease as well. The fungus is ubiquitous in the environment and flourishes in rotting vegetation and decaying organic material.

The disease is contracted as the result of inhalation of spores. It may also be contracted by oral ingestion, especially if birds are fed moldy seed. The fungus is also capable of penetrating broken skin and egg shells, and so is able to infect a developing embryo.

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. Ataxia and paralysis occur of the central nervous system is affected.

Next time: Diagnosis of Aspergillosis.