Saturday, February 9, 2008


Aspergillosis is an infection of the respiratory system that occurs sporadically in a wide range of birds. Birds from cold and dry climates are highly susceptible to infection. Environments that are conducive to the environmental growth of Aspergillus spp. and environments that are poorly ventilated will result in an increased incidence of aspergillosis. Disease can be localized to the upper airways or the syrinx, or it may involve the air sacs and lungs. Respiratory signs are a common feature of this disease, but a bird may not manifest signs until the disease is advanced. Radiographs, endoscopy and biopsy, cytology and hematology are all valuable tools in the diagnosis of this disease. Even with all these assays, the diagnosis of aspergillosis is often a difficult one.

The diagnosis of aspergillosis has been most extensively studied in humans. Ancillary diagnostic assays used in people include PCR to detect Aspergillus DNA from blood, an ELISA to detect Aspergillus antigen and an ELISA to detect anti-Aspergillus antibody. These studies clearly indicate that even a combination of these three assays will not be adequate to detect many cases of aspergillosis. The problem comes from the fact that most people who contract aspergillosis are immunocompromised. This also may be true in birds. If the infected person's immune system is adequate to contain the disease and the organism is localized in a walled-off granuloma, then these individuals are found to produce antibody. People with generalized disease are generally severely immunocompromised and they do not produce antibody. In these people, Aspergillus antigen and DNA are most likely to be found in the blood, but they are not when the lesion is encapsulated. If the pathophysiology of avian aspergillosis resembles that seen in humans, then none of these assays are likely to detect infection in most infected birds. A combination of these assays may be more specific, but false negatives are to be expected.

Reference: "Clinical Avian Medicine - Vol I and II" by Harrison and Lightfoot