Avian Aspergillosis

Serodiagnostics for Avian Aspergillosis

Aspergillus is a common fungus known to infect various mammals and birds. Many species of captive birds appear especially susceptible to infection. Early diagnosis and treatment are not always possible as advanced stages of disease may be present before significant clinical signs develop prompting veterinary attention. Antemortem diagnostics including traditional techniques such as routine hematology and chemistry may be used but changes may be non specific for aspergillosis. Lesions consistent with aspergillosis may be observed by radiography. Endoscopy is an excellent tool but may not be available or may not be advisable if the patient is very ill. Thus, diagnosis remains challenging and problematic. Antemortem serological tests are available and have been demonstrated to have diagnostic and prognostic value.

Testing for Antibody
We have reported that waterfowl, penguin, and raptor groups demonstrate the highest antibody reactivity with a mean index of 1.8 or greater. This contrasts the poor antibody production in psittacine which averages 1.2 which is considered a negative result in our assay. In a study of birds with probable and confirmed aspergillosis (with a sample set dominated by psittacine patients), a significant difference in antibody titer was observed between normal and confirmed groups. However, it should be noted that the mean index of the confirmed group only fell into the weakly positive qualitative score. We conclude that the use of antibody testing alone is not of diagnostic value.

Testing for Galactomannan
Recently, a commercial assay to measure galactomannan, a major antigen of Aspergillus, has been applied to human clinical medicine with reports of a variable sensitivity and specificity reaching upwards of 100% often dependent on whether the patients were receiving antifungal treatment and if they had a proven or probable diagnosis. In animal studies using a rabbit and rodent models of infection, the test yield both high sensitivity and specificity. In our laboratory we have found that birds with confirmed aspergillosis averaged 26 fold higher levels of galactomannan than believed normal birds. Those with suspected infection were nearly 2 fold higher. As the index increases, the specificity increases but the sensitivity decreases. The overall test sensitivity was 67% and the specificity was 73%.

In our laboratory experience, we often observed negative galactomannan levels in the presence of high antibody levels. We propose the circulating antibody effectively complexes and clears the galactomannan preventing its detection in the assay. Thus, the use of galactomannan testing is limited in birds with an antibody index of greater than 2.0. This concept was recently supported by the work of Drs. Jankowski and Adkesson at the Brookfield Zoo which was presented at the 2011 AAZV conference. Using a large sample set, they found rare galactomannan positive results in the high antibody producing penguin species.

Protein Electrophoresis
While not diagnostic of aspergillosis, the presence of globulinopathies in samples from avian patients is strongly supportive of the presence of disease. In a study group dominated by psittacine species, the most common electrophoretic change is an increase in beta globulins (40%) followed by beta/gamma globulin increases (18%) and gamma globulin increases alone (9%). Notably, 28% of those birds with confirmed aspergillosis demonstrated no electrophoretic abnormalities. This may reflect the advanced stage of infection and disease and a possible anergic state of the immune system. Test sensitivity and specificity were found to be 73% and 70%, respectively. Significant changes in the protein electrophoretogram as well as in serum amyloid A levels were observed in experimentally infected falcons.

Aspergillus Panel
The use of the Aspergillus Panel approach to testing does give additive sensitivity. For example, the use of the galactomannan assay with protein electrophoresis increased test sensitivity to 89%. As the panel may be used to diagnose patients at some unknown point in the disease process and with potential previous treatment regimens, each panel component can provide its own value. For example, the presence of antibody in a psittacine patient would be considered highly unusual and should result in further follow up. Likewise, the presence of galactomannan in a chronically ill bird would be significant as these birds often are not high antibody producers. Protein electrophoresis, at all times, provides a reflection of an ongoing acute phase response and, if abnormal, provides valuable data that can be used for prognostication.

Additional Reading

C. Cray. “Diagnosis of aspergillosis in avian species” in Fowler’s Zoo and Wild Animal Medicine: Current Therapy, Eds. M. Fowler and E. Miller, 7TH edition, Elsevier, Inc., pp 336-342, 2011.

M. Franca, C. Cray, and H.L. Shivaprasad. Serological testing for aspergillosis in broiler chickens and commercial turkeys. Avian Diseases, 56(1):160-164, 2012.

C. Cray. New testing options for the diagnosis of avian aspergillosis. ExoticDVM 12(1): 32-34, 2010.

C. Cray. New testing options for the diagnosis of avian aspergillosis. Part II: Clinical interpretation of aspergillosis test results. ExoticDVM 12(2): 29-31, 2010.

C. Cray, D. Reavill, A. Romagnano, F. Van Sant, D. Champagne, R. Stevenson, V. Rolfe, C. Griffin, and S. Clubb. Galactomannan assay and protein electrophoresis findings in psittacine birds with aspergillosis. Journal of Avian Medicine and Surgery, 23(2):125-135, 2009.

C. Cray, T. Watson, and K. Arheart. Serosurvey and diagnostic application of antibody titers to Aspergillus in avian species. Avian Diseases, 53:491-494, 2009.

C. Cray, T. Watson, M. Rodriguez, K. Arheart. Application of galactomannan analysis and protein electrophoresis in the diagnosis of aspergillosis in avian
species. Journal of Zoo and Wildlife Medicine, 40(1):64-70, 2009.

D. Fischer, L. Van Waeyenberghe, C. Cray, M. Gross, E. Usleber, F. Pasmans, A. Martel, and M. Lierz. Comparison of diagnostic tools for the detection of aspergillosis in blood samples of experimentally infected falcons. Avian Diseases, 58:587-598, 2014.