Key Points

• Aspergillus fumigatus is a ubiquitous organism that grows best in a warm, moist environment.
• Factors that may promote the growth of Aspergillus spp. include the presence of organic debris like moist bedding, prolonged antibiotic administration, poor sanitation, poor ventilation, and endogenous steroid production secondary to stress or the administration of exogenous steroids.
• Aspergillosis most frequently causes air sacculitis and pneumonia, but almost any organ system can be affected.
• Companion bird species most frequently diagnosed with aspergillosis include African Grey, Amazon, and Pionus parrots.
• The most important fungal disease of juvenile birds is candidiasis. Candida albicans can overgrow in the oropharynx or crop leading to anorexia, oral plaques, ingluvitis, and regurgitation.
• The presence of avian gastric yeast or Macrorrhabdus ornithogaster may be incidental, or may be associated with depression, weight loss, anorexia, and regurgitation, particularly in small parrots or songbirds.