Avian Aspergillosis Study Guide

Overview and Clinical Importance

Aspergillosis is the most common fungal infection in birds and represents a major cause of morbidity and mortality in both captive and wild avian species. This opportunistic mycosis is caused primarily by Aspergillus fumigatus (accounting for approximately 95% of cases), with A. flavus, A. niger, and A. terreus occasionally implicated. Understanding this disease is critical for NAVLE success as it frequently appears in questions regarding avian medicine, particularly concerning respiratory disease in psittacines, raptors, and waterfowl.

The infection typically affects the respiratory tract (lungs and air sacs) but can disseminate to virtually any organ system. The ubiquitous nature of Aspergillus spores in the environment means that exposure is constant; however, clinical disease develops only when host defenses are compromised or when overwhelming spore exposure occurs.

Etiology

Causative Organisms

Aspergillus fumigatus is the predominant species causing avian aspergillosis, responsible for up to 95% of clinical cases. This thermophilic fungus thrives at body temperature (37-50°C), making it particularly well-adapted to infect warm-blooded hosts. The organism belongs to the phylum Ascomycota and produces characteristic septate, dichotomously branching hyphae with acute-angle (approximately 45-degree) branching patterns.